bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunofluorescent localization of a Ca2+-dependent neutral protease in hamster muscle
Authors: Barth R. , Elce J. S.
Published: December 2017

A Ca2+-dependent neutral thiol protease is widely distributed in mammalian tissues and has been implicated in muscle protein turnover. As a first step to understanding the physiological function of this enzyme, its cellular and subcellular localization has been studied in hamster cardiac and skeletal muscle by means of indirect immunofluorescence. The results showed that the Ca2+-dependent protease is located either at the plasma membrane or in the connective tissue matrix that surrounds the muscle cels. The uniform distribution along membranes and around capillaries indicated that the protease is not confined to connective tissue cells. This evidence, together with the Ca2+-dependence of the enzyme, suggests a distribution throughout the extracellular connective tissue of the muscle. In this position, it would seem unlikely that the enzyme could participate in protein turnover within muscle cells in normal tissue.
Effects of estradiol and progesterone on food intake, body weight, and carcass adiposity in weanling rats
Authors: Schwartz S. M. , Wade G. N.
Published: December 2017

The effects of estradiol and progesterone on food intake, body weight, carcass adiposity, and adipose tissue lipoprotein lipase (LPL) activity were investigated in weanling female rats. Treatment with estradiol benzoate (EB) reduced body weight gain in ovariectomized (OVX) weanlings as it does in adults. However, other responses to EB were attenuated or absent in weanlings. EB treatment did not reduce food intake, carcass adiposity, or adipose tissue LPL activity. This impaired responsiveness to EB may be due to decreased levels of cytoplasmic estrogen receptors in liver and adipose tissue (but not hypothalamus) in weanlings. On the other hand, responsiveness to progesterone was adultlike in weanlings. Treatment of OVX, EB-primed weanlings with progesterone increased food intake, body weight gain, and carcass adiposity. This adultlike responsiveness to progesterone was associated with adultlike levels of adipose tissue progestin receptors. However, progesterone treatment did not increase adipose tissue LPL activity in weanlings, indicating that changes in LPL activity are not necessary for progesterone-induced obesity.
Perifusion of rat pituitaries: requirements for optimal GnRH-stimulated LH release
Authors: Stern J. E. , Conn P. M.
Published: December 2017

Perifusion of rat hemipituitaries was used as an in vitro model for luteinizing hormone (LH) release in response to gonadotropin-releasing hormone (GnRH). LH release during continuous stimulation with GnRH (10(-7) M) was inhibited by EGTA (1.5 or 5 mM given 1 h prior to GnRH) or by D-600 (methoxyverapamil, 1 mM, given concomitantly with GnRH). These findings suggested that GnRH-stimulated LH release was a Ca2+-dependent process. Inhibition of LH release caused by Ca2+ chelation with EGTA was reversed when hemipituitaries were returned to medium without EGTA. Elevation of medium K+ (to 50 mM, without GnRH) stimulated Ca2+-dependent LH release during the 1st h. GnRH-stimulated LH release was 60% inhibited by cycloheximide (25 micrograms/ml) after the 1st h. LH release was not stimulated by dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP), although this cyclic nucleotide was shown to have biological activity and to enter pituitary cells as judged by its ability to stimulate prolactin release from the same tissue. The data suggest that optimal LH release in response to GnRH requires extracellular Ca2+ and depends on protein synthesis.
Lung as a model for evaluation of critical intracellular PO2 and PCO
Authors: Fisher A. B. , Dodia C.
Published: December 2017

The relationship between cellular metabolism and tissue O2 tension was investigated using the isolated perfused rat lung. Lungs were ventilated with gas mixtures of varying PO2 under conditions of no net gas exchange so that alveolar and lung parenchymal gas tensions were in approximate equilibrium. When alveolar PO2 was reduced to 0.7 mmHg, there were significant increases in lung lactate production and perfusate lactate/pyruvate, and decreases in lung tissue ATP content and ATP/ADP. Metabolic parameters were unchanged by alveolar hypoxia when alveolar PO2 was 7 mmHg or greater. Changes of complete anoxia required a PO2 less than 0.04 mmHg. To determine competition between O2 and CO in lung metabolism, alveolar O2 was maintained at 5% and CO was varied from 0 to 90%. Significant changes in production of lactate and pyruvate and tissue ATP content occurred with an alveolar CO of 75% (CO/O2 = 15) but not with CO concentrations of 50%, (CO/O2 = 10) or less. These results with an intact organ confirm previous data with subcellular systems showing a high affinity of the mitochondrial respiratory chain for O2, and indicate that the metabolic changes of hypoxia do not occur until intracellular PO2 approaches 1 mmHg or the CO/O2 exceeds 10.
Role of follicle wall in meiosis reinitiation induced by insulin in Rana pipiens oocytes
Authors: Lessman C. A. , Schuetz A. W.
Published: December 2017

The involvement of the ovarian follicle wall in insulin induction of Rana pipiens oocyte maturation in vitro was examined. Complete removal of the follicle wall significantly decreased, but did not obliterate, oocyte maturation (i.e., germinal vesicle breakdown, GVBD) induced by insulin. Dose-response studies of GVBD induction revealed that oocytes within intact follicles were at least 100 times more sensitive to insulin than denuded oocytes. Addition of cyanoketone, a steroid biosynthesis inhibitor, to intact follicles also suppressed insulin-induced GVBD. Inhibitory effects of either follicle wall removal or cyanoketone were not observed when denuded oocytes were treated with progesterone. Addition of either progesterone or pregnenolone to insulin-treated denuded oocytes augmented the oocyte GVBD response compared to either steroid alone and essentially replaced the effect of the follicle wall. In summary, steroidogenesis in the follicle wall appears to be a major factor contributing to the ability of insulin to induce GVBD. However, whether insulin stimulates follicle wall steroidogenesis or simply augments the biological activity of endogenous basal steroid levels is unresolved. The in vitro results show that oocyte maturation can be modulated by the combined actions of several hormones. Such steroid-insulin interactions may also be relevant to understanding the control of oocyte maturation in amphibians and other vertebrates, including mammals, under physiological conditions in vivo.
Localization and characterization of adrenergic receptors on frog skin melanophores
Authors: Longshore M. A. , Horowitz J. M.
Published: December 2017

The functional location of adrenergic binding sites was studied in frog skin melanophores by injecting norepinephrine (NE) outside and inside a melanophore. In 49 groups of cells (75% of the fields tested) iontophoretic injection of NE outside the cell caused melanosome aggregation in the target cell and/or in the field. In six cells in which a resting membrane potential was measured before and after intracellular injection (10-90 nA), NE elicited no change in melanosome configuration. Once the receptors were localized, the effect of temperature on these receptors was determined by measuring the reflectance of skins (an indication of melanosome aggregation or dispersion) in two populations of frogs treated with NE, Rana pipiens pipiens (with dominant alpha-receptors) and Rana berlandieri forreri (with dominant beta-receptors). NE (0.1 mM) caused melanosome aggregation in the former and dispersion in the latter tested at 12, 22, and 40 degrees C. The iontophoretic and reflectance results suggest that the binding site of the adrenergic receptor is located on the outer surface of the plasma membrane of melanophores and that alpha- and beta-receptors evoke aggregation and dispersion, respectively, within the temperature range of these experiments.
Lipoprotein lipase activities in adipose tissues and muscle in the obese Zucker rat
Authors: Hartman A. D.
Published: December 2017

Activity of lipoprotein lipase (LPL) was determined in whole adipose tissue and isolated adipocytes, and in heart and skeletal muscle that contained predominantly red or white fiber types in lean and obese Zucker rats. In rats of both sexes at 9-11 and 26-30 wk of age, no differences were observed between lean and obese rats when LPL activity of the perirenal (PR), subcutaneous (SC), and mesenteric (M) adipose tissues was expressed per millimole of tissue triglyceride. Within each sex, data relating the LPL content of isolated adipocytes to cell size was a linear function in which data for lean and obese rats fell on the same regression line. Measurement of the distribution of adipose tissue LPL activity between adipocytes and other tissue constituents showed no differences between lean and obese rats, a finding that is inconsistent with the hypothesis that obesity results in part by an alteration in adipose tissue enzyme distribution. Activity of LPL in the myocardium and red fiber types in the younger group of both sexes showed significant decreases in obese animals. This was also true for white fibers of males but not females. No differences in heart or muscle LPL between lean and obese rats were observed in the older group of either sex.
Effects of starvation and obesity on somatostatin, insulin, and glucagon release from an isolated perfused organ system
Authors: Boden G. , Baile C. A. , McLaughlin C. L. , Matschinsky F. M.
Published: December 2017

We have studied the effects of starvation and of obesity on somatostatin, insulin, and glucagon release from an isolated perfused organ system in fed and 3- and 5-day fasted Holtzman rats and in obese (fa/fa) and lean (Fa/?) Zucker rats. Fasting for 3 days significantly decreased basal (-71%) and amino acid-stimulated (-62%) somatostatin output. After 5 days of starvation, there was a significant increase over the 3-day level in somatostatin output stimulated by amino acid plus glucose (+540%) and by amino acids plus tolbutamide (+238%). Three and five days of starvation severely depressed insulin output while having no statistically significant effects on glucagon secretion. Somatostatin output from obese Zucker rats was significantly greater than that from lean controls in response to amino acids (41.2 +/- 13.2 vs. 16.3 +/- 10.3 ng/25 min, P less than 0.05). Insulin output was greatly increased from obese compared to lean Zucker rats, whereas there were no statistically significant differences in glucagon output. These data show that fasting decreases and obesity increases both somatostatin and insulin release. They suggest that altered stimulation by nutrients was primarily responsible for changes in somatostatin and insulin release observed in starving and obese rats.
Postovulatory steroidogenesis after PMS-induced ovulation in immature female rats
Authors: Taya K. , Greenwald G. S.
Published: December 2017

Thirty-day-old rats given a single subcutaneous injection of 5 IU pregnant mare serum gonadotropin (PMS) at 0900 h ovulated on the morning of day 33 (= estrus). However, the second ovulation did not occur until 9.4 days later. To determine the mechanism responsible for the delay in the second ovulation, in vivo and in vitro determinations of steroid and peptide hormones were compared between PMS-primed immature rats and adult cyclic rats. In PMS-primed rats, the corpora lutea (CL) produced progesterone for 2 days longer (until day 36) than the CL of the adult rat. Serum levels of 20 alpha-dihydroprogesterone, testosterone, and estradiol in PMS-primed rats were significantly lower than the corresponding values in adult rats. Serum LH was consistently lower in the PMS-primed rats. An increase in serum FSH occurred on days 36–37, which may be responsible for maturation of the follicles destined to ovulate at the second ovulation. On day 37, the nonluteal ovary of the PMS-primed rats also began to produce in vitro appreciable amounts of testosterone and estradiol. These findings suggest that the greater levels of prolactin and/or low levels of luteinizing hormone during estrus in PMS-primed rats may be responsible for the prolonged secretion of progesterone by the CL. This in turn inhibits follicular maturation, indirectly by lowering serum LH, which is reflected in reduced ability of the follicles in vitro to produce testosterone and estradiol until the CL regress.
Evidence for a photoperiod-sensitive pacemaker for estrous cycle of the rat
Authors: Yochim J. M. , Shirer H. W.
Published: December 2017

To define how the periodicity of light regulates reproductive cyclicity in the rat, animals were exposed to slightly altered photoperiods in which the light/dark ratio was maintained as in the control (14L + 10D) environment. Exposure to a 22.5-h photoperiod (13.125L + 9.375D) for 10–80 days induced a significant prolongation of the first and all subsequent vaginal cycles by about 30 h. Ovulation in these animals was normal. By contrast, exposure to a 26-h photoperiod (15.167L + 10.833D) had no significant effect on vaginal cyclicity. A comparison of the data with theoreticaly generated results revealed that a significant prolongation of the estrous cycle under conditions of a shortened photoperiod cannot be accounted for by a simple entrainment of the estrous cycle to the timing of the new circadian rhythm. Rather, the evidence suggested that a photoperiod-entrained rhythm may interact with a second rhythm of different periodicity to alter the duration of the reproductive cycle as measured in this study.
Pubertal endocrinology of the baboon: adrenarche
Authors: Castracane V. D. , Cutler G. B. , Loriaux D. L.
Published: December 2017

The concentration of the adrenal steroids dehydroepiandrosterone (DHA) and dehydroepiandrosterone sulfate (DHA-S) was measured by radioimmunoassay in plasma of 134 baboons (Papio cynocephalus) from 0 to 17 yr of age. Plasma androstenedione (delta 4-A) was also measured in 289 baboons encompassing the same age range. The concentration of DHA was persistently high from birth to adulthood, exceeding 700 ng/dl at all ages. This differs markedly from the human pattern in which DHA concentrations fall below 50 ng/dl following regression of the fetal adrenal. Plasma DHA-S declined rapidly during the first 2 yr of life, causing a significant age-related decline in the ratio of DHA-S:DHA, a pattern not seen in man. Plasma delta 4-A declined during the first 3 yr, but remained greater than 100 ng/dl. delta 4-A then rose sharply at age 4, the time of gonadal maturation in the baboon. Thus, the baboon differs from man primarily in the persistent elevation of plasma DHA and delta 4-A prior to puberty. It remains to be determined whether this difference reflects fundamentally different mechanisms regulating adrenal androgen secretion or merely the closer temporal juxtaposition of fetal adrenal regression and adrenarche due to the more rapid sexual maturation of the baboon.
Importance of glucagon in mediating epinephrine-induced hyperglycemia in alloxan-diabetic dogs
Authors: Perez G. , Kemmer F. W. , Lickley H. L. , Vranic M.
Published: December 2017

In normal dogs epinephrine stimulates glucose production (Ra) independently of glucagon. To investigate the role of this interaction in diabetes, epinephrine (0.1 micrograms . kg-1 . min-1) was infused for 90 min in five alloxan-diabetic dogs in the presence or absence of somatostatin (0.1 micrograms . kg-1 . min-1). In response to epinephrine, glycemia rose by 40% reflecting a near maximal (122%) increase in Ra. Plasma glucagon (IRG) rose to 953 pg/ml, whereas insulin (IRI) increased minimally. When somatostatin was infused with epinephrine to prevent the rise of IRG and IRI, there was only a marginal increase of glucose concentration (12%) and production (38%). The effect of somatostatin was reversed by infusing glucagon (10 ng . kg-1 . min-1) together with epinephrine and somatostatin into five additional alloxan-diabetic dogs. Increments in IRG, glycemia, and Ra were fully reestablished. A 100% FFA increase was observed in all three groups, indicating that the lipolytic effect of epinephrine was independent of glucagon. In conclusion, in diabetic dogs, in contrast to normal dogs, epinephrine induced a marked and prolonged increase in glucose concentration and production mostly through a stimulation of IRG secretion.
Reversible hyperinsulinuria in diabetic ketoacidosis in man
Authors: Sacks H. , Rabkin R. , Kitabchi A. E.
Published: December 2017

Urinary clearance and fractional urinary clearance of immunoreactive insulin (IRI) and beta 2-microglobulin (I beta 2M) were studied in patients with diabetic ketoacidosis (DKA) before, during, and after treatment. Our results indicate that in DKA in man a) there is an approximate 250-fold increase in urinary and fractional urinary clearance of IRI and a 600-fold increase in urinary and fractional urinary I beta 2M clearance, which suggests that the hyperinsulinuria is secondary to a nonspecific defect in tubular luminal uptake of low-molecular-weight proteins, although decreased IRI degradation cannot be excluded; b) because increased IRI clearance is not changed by the pharmacologic plasma IRI levels achieved, the residual tubular absorptive capacity is not saturable; c) I beta 2M clearance but not IRI clearance is significantly improved by the time metabolic control is attained, suggesting separate tubular transport systems; d) a small, therapeutically insignificant fraction of the infused insulin is lost in the urine during therapy of DKA; and e) defective renal tubular luminal uptake (and possibly degradation) of IRI is reversible.
Transepithelial electrophysiology of cultured mouse mammary epithelium: sensitivity to prolactins
Authors: Bisbee C. A.
Published: December 2017

Several prolactins and growth hormones affect cultured BALB/c mouse mammary epithelial electrophysiology at doses of 10 micrograms/ml. Ovine prolactin is effective at doses as low as 1 ng/ml, levels that are three to four orders of magnitude less than effective amounts of rat growth hormone. Because growth hormone preparations may have approximately 1% prolactin contamination, its effects are probably due to prolactin contamination. The maximum effect of ovine prolactin on short-circuit current and on resistance occurs at doses differing by two orders of magnitude, indicating that these two effects of prolactin may be partially separable. Therefore, prolactin may have effects on passive permeability properties in addition to its documented effects on active transport.
Role of thyroxine in coordinate control of corticosterone and CBG in postnatal development
Authors: D'Agostino J. , Henning S. J.
Published: December 2017

The role of thyroxine (T4) in the ontogeny of serum corticosteroid-binding globulin (CBG) and corticosterone has been studied in the rat. Daily injection of T4 (0.1 micrograms/g body wt) resulted in the precocious appearance of both CBG and corticosterone. A dose-response study revealed an increase in both CBG and corticosterone at thyroxine doses greater than 0.02 micrograms/g body wt. In propylthiouracil-induced hypothyroid pups, the developmental rise of both CBG and corticosterone was suppressed. To determine whether T4 elevation of CBG was mediated by corticosterone, serum CBG was measured in corticosterone-injected pups (10 micrograms/g body wt). No increase in CBG was detected on days 8 and 10. A slight increase, only one-eighth that elicited by T4, occurred on day 12. There was also no synergistic effect between T4 and corticosterone. We conclude that the postnatal increase in serum T4 concentrations cues the developmental rise of both CBG and corticosterone in the rat.
Alterations in rat adipose tissue morphology induced by a low-temperature environment
Authors: Miller W. H. , Faust I. M.
Published: December 2017

Rats raised in the cold showed an unusual pattern of adipose tissue morphology. Male Sprague-Dawley rats were maintained in a 5 degrees C environment for up to 24 wk and the cellularity of their major adipose depots was determined. Normal age-related increases in adipocyte number were absent in two major fat depots (retroperitoneal and inguinal), whereas there was a supranormal increase in a third (epididymal). This pattern of hyperplasia contrasts sharply with that seen in rats fed highly palatable high-fat or high-carbohydrate diets in which retroperitoneal depots show the most hyperplasia and epididymal pads the least. Such variations of response across depots suggest that the features of adipose tissue responsible for adipocyte proliferation in the various depots may not be homogeneous both in their nature and in their distribution.
Renal parathyroid hormone receptors in the chick: downregulation in secondary hyperparathyroid animal models
Authors: Forte L. R. , Langeluttig S. G. , Poelling R. E. , Thomas M. L.
Published: December 2017

We characterized the binding of 125I-[Nle8, Nle18, Tyr34]parathyroid hormone-(1-34) amide [125I-nlPTH-(1-34)] to renal plasma membranes prepared from chicks to determine the effects of secondary hyperparathyroid states on renal PTH receptors. This radioligand exhibited specific binding to membranes with high affinity (Kd, 2-3 X 10(-9) M). Agonists or competitive antagonists of PTH were effective in competing for binding sites labeled with 125I-nlPTH-(1-34), whereas an inactive fragment of PTH, salmon calcitonin, and bovine growth hormone did not compete with the radioligand for renal PTH receptors. Newly hatched chicks raised on control diet with adequate vitamin D and calcium or diets deficient in either vitamin D or calcium were used to study the regulation of renal PTH receptors in experimental models of secondary hyperparathyroidism. We found that both experimental diets resulted in marked hypocalcemia and progressive loss of renal cyclic AMP responsiveness to PTH in vitro. Associated with this refractoriness to the hormone was a marked reduction in PTH receptors in membranes from both vitamin D-deficient and calcium-deficient chick kidney. No change in the affinity of the PTH receptors was found. Vitamin D3, in a single dose of 250 micrograms, partially restored serum calcium of vitamin D-deficient birds toward normal by 72 h and also partly restored renal cyclic AMP responsiveness to PTH and the PTH receptor number toward control values. We conclude that renal refractoriness to PTH observed in experimentally hyperparathyroid animals models is due to a marked loss of plasma membrane receptor sites for PTH without an apparent change in the affinity of the receptors for the hormone.
Intracellular Na+ and K+ activities during insulin stimulation of rat soleus muscle
Authors: Stark R. J. , O'Doherty J.
Published: December 2017

The action of insulin on the resting membrane potential (Em) and intracellular sodium and potassium activities (aNa, aK) of rat soleus muscle fibers was determined by direct intracellular measurements of aNa, aK, and Em using Na-selective, K-selective, and conventional microelectrodes. The use of these microelectrodes allowed us to continuously monitor these parameters in the same fiber. Although we were able to accurately measure aNa and aK and continuously monitor their levels throughout periods of insulin stimulation of up to 20 min duration, we were unable to detect any significant change in Em, aNa, or aK. Varying the concentration of insulin or extracellular glucose failed to alter our observations. These results indicate that the action of insulin on the sarcolemma and subsequent increase in glucose transport must result from some mechanism independent of a change in membrane potential or intracellular sodium or potassium activity.
Development of pancreatic and plasma insulin in prenatal and suckling Zucker rats
Authors: Turkenkopf I. J. , Johnson P. R. , Greenwood M. R.
Published: December 2017

Pancreatic and plasma insulin concentrations in preobese and lean Zucker rats were determined during three developmental periods: 1) gestation, 2) suckling, and 3) postweaning. Individual fetal samples were derived from two types of matings: 1) homozygous obese males (fafa) with heterozygous females (Fafa), and 2) homozygous lean males and females (FaFa). Suckling and postweaned pups from similar matings were partially pancreatectomized, tail bled, and identified retrospectively. In 21-day-old fetuses bearing the fa gene, plasma insulin concentration was elevated (P less than 0.001) and pancreatic concentration was slightly lower (P less than 0.05) compared to homozygous lean fetuses. Neither pancreatic nor plasma insulin concentration differed between preobese and lean pups during suckling, except that pancreatic concentration became elevated in preobese pups on postnatal day 20 (P less than 0.05). Plasma insulin concentration was elevated 24 h postweaning (P less than 0.01). These data support the hypothesis that the fa gene initiates metabolic changes during gestation that are modulated during suckling, but reappear at weaning. The data also establish that increased adipocyte size and lipoprotein lipase activity in 7- to 12-day-old preobese pups are not dependent on concomitant hyperinsulinemia.
Parathyroid, renal, and skeletal responses to induced hypocalcemia in the dog
Authors: Fox J. , Heath H.
Published: December 2017

This study was designed to determine 1) whether the plasma immunoreactive parathyroid hormone (IPTH) response to acutely attained, constant (8 h) hypocalcemia is biphasic, and 2) if so, how kidney and bone respond to these changing plasma IPTH levels. We initiated constant hypocalcemia (decrement of Ca, 1.7 mg/dl) in six conscious dogs using the "calcium clamp" technique. Plasma IPTH concentrations increased maximally (fivefold) within 15 min and then decreased gradually over 1 h to a constant, but still elevated level (3.2-fold increase). Urinary excretion of phosphate and hydroxyproline increased more slowly, reaching plateaus at 1.75 h (76% increase) and 5.5 h (70% increase), respectively. The EGTA infusion rate required to maintain constant hypocalcemia was virtually constant (85 +/- 9 mumol.kg-1.h-1) after 20 min and corresponded to skeletal release of about 80 mg Ca.kg-1.day-1. The contribution of the kidney in conserving filtered calcium was relatively minor (2.0 +/- 0.5 mumol.kg-1.h-1). These data demonstrate that the parathyroid response to acute, constant hypocalcemia is biphasic and is temporally divergent from the uniphasic phosphaturic and hydroxyprolinuric responses. The ensuing increased skeletal release of calcium is very high and is maximal within minutes.
Mineralocorticoid activity of 19-nor-DOC and 19-OH-DOC in adrenalectomized rat
Authors: Perrone R. D. , Bengele H. H. , Dale S. L. , Melby J. C. , Alexander E. A.
Published: December 2017

Excess mineralocorticoid activity is thought to be responsible for the increased sodium reabsorption found after adrenal enucleation, but no known mineralocorticoid has been demonstrated in quantities sufficient to account for this antinatriuresis. 19-Hydroxydeoxycorticosterone (19-OH-DOC) has been synthesized by the incubated enucleate adrenal capsule and 19-nordeoxycorticosterone (19-nor-DOC), a possible metabolite, has been found in the urine of rats with regenerating adrenal glands. To evaluate the in vivo mineralocorticoid potency of these steroids, we studied glucocorticoid-replete adrenalectomized rats and measured the sodium and potassium excretion after administration of these steroids. Our results indicate that 19-nor-DOC has equipotent antinatriuretic activity compared to aldosterone but was less kaluretic. 19-OH-DOC had no significant antinatriuretic or kaluretic activity. We conclude that 19-nor-DOC is a potent mineralocorticoid and may be responsible for the enhanced sodium reabsorption found after adrenal enucleation.
Hormonal changes associated with hypertension in neoplasia-induced hypercalcemia
Authors: Sowers J. R. , Barrett J. D.
Published: December 2017

Neoplasia-induced hypercalcemia in the Fischer rat results in hypertension 1 wk after Leydig cell tumor transplantation. Systolic blood pressure, plasma catecholamine, prolactin, plasma renin activity (PRA), and aldosterone responses to immobilization stress were evaluated in Fischer rats 10 days after tumor transplantation and in age-matched nontransplanted controls. Basal systolic blood pressure, norepinephrine, and PRA levels at 10 days after tumor transplantation were higher in association with elevated calcium levels in tumor-transplanted rats than in controls. Systolic pressure, norepinephrine, and epinephrine responses to immobilization stress were greater in the hypercalcemia 10-day transplanted rats. Although basal levels of prolactin and aldosterone were similar in the two groups. These observations suggest that elevated levels of the vasoactive hormones norepinephrine and angiotensin may play a pivotal role in development of hypertension in association with neoplasia-induced hypercalcemia. Further, neoplasia-induced hypercalcemia in the Fischer rat is associated with a relative hyperreninemic hypoaldosteronism state.
Glucose transport in adipocytes and its control by growth hormone in vivo
Authors: Schoenle E. , Zapf J. , Froesch E. R.
Published: December 2017

Previous results showed maximally enhanced basal glucose transport in adipocytes of hypophysectomized rats and restoration to normal after human growth hormone (hGH) administration. The data suggested a hGH-dependent "limiting factor" for glucose transport in the adipocyte membrane, which is acutely inhibited by insulin resulting in enhanced glucose transport. In this study the effect of hGH was investigated with respect to dose and time dependence. hGH was administered by continuous infusion from subcutaneously implanted Alzet minipumps. A significant decrease of basal glucose transport was obtained at the lowest hGH dose of 50 mU/day for 6 days. This effect of hGH was strictly correlated to the effects on growth (tibial epiphyseal width, DNA synthesis, body weight, serum level of insulin-like growth factor). The effect of hGH on basal glucose transport was already observed after 12 h of infusion, and it increased to a maximum after 3 days. The data support the concept that GH regulates the glucose transport system in adipose tissue in vivo.
Electromechanical responsiveness of hyperthyroid cardiac muscle to beta-adrenergic stimulation
Authors: Wei J. Y. , Spurgeon H. A. , Lakatta E. G.
Published: December 2017

The effect of isoproterenol (5 x 10(-10)-10(-6) M) on simultaneous measurements of the transmembrane action potential (TAP) and isometric twitch were made in thin right ventricular papillary muscles isolated from hyperthyroid (H) and euthyroid (E) rats. In response to low concentrations of isoproterenol (less than 5 x 10(-9) M) both TAP depolarization above -40 mV and twitch tension were significantly enhanced in H (30 and 50% above base line, respectively) but were not changed in E. The maximum catecholamine-induced change in twitch tension and TAP was not different in H versus E. However, over the entire dose-response curve to isoproterenol, the relaxant effects of the catecholamine, i.e., shortening of the times from stimulus to peak tension (TPT) and from stimulus to half-relaxation of tension (RT 1/2) that accompanied twitch potentiation and TAP changes in E did not occur in H. In contrast to the absence of a relaxant effect on these twitch duration parameters in H, the rate of tension decay of the terminal part of the twitch was enhanced in H to an extent equal to that in E. The results suggest that 1) in response to low levels of beta-adrenergic stimulation, enhanced TAP depolarization above -40 mV, which occurs in H but not in E, mediates the twitch potentiation that occurs in H but not in E; 2) the cellular mechanisms that mediate twitch potentiation and action potential changes in response to beta-adrenergic stimulation are independent of those that control the relaxant effect to shorten TPT; and 3) factors through which catecholamines enhance the rate of tension decay in the terminal phase of the contraction cycle are independent of those that reduce TPT and RT 1/2; thus beta-adrenergic stimulation appears to have a "dual" relaxant effect on the myocardium.
Binding, degradation, and bioactivity of insulin in primary cultures of rat hepatocytes
Authors: Varandani P. T. , Darrow R. M. , Nafz M. A. , Norris G. L.
Published: December 2017

Hepatocytes from fasted rats, previously maintained as a monolayer in a serum-free glucagon-containing culture medium are demonstrated to provide a useful model system for the study of receptor-mediated mechanisms of insulin action. The cultured liver cells show glucagon- and insulin-responsive biological effects. These cultures show the long-term effects of insulin on the syntheses of protein ([3H]leucine incorporation), glycogen, and lipids (conversion of [3H]glucose) in a dose-dependent manner in the physiological range of insulin concentrations. The order of the effects of different analogues of insulin on each of the bioactivities studied at 37 degrees C is the same as their order to compete at 25 degrees C for binding to insulin-specific receptors. The characterization of radioactive products of 125I-insulin using gel filtration and anti-insulin A chain antibody has shown a transient accumulation of insulin A chain, indicating that the sequential pathway of insulin degradation is operative in the anchored, cultured hepatocytes. Whereas the synthesis of proteins proceeds linearly after insulin inoculation, the syntheses of glycogen and lipids first occur after a lag period of about 10 and 12 h, respectively. None of the three 125I-labeled fragments or products of 125I-insulin released in the culture mediums showed any biological activity (glycogenesis) in cultured hepatocytes although a high-molecular-weight 125I-product isolated from cells could not be tested because of its insolubility. The possibility that the insulin effects might have been mediated via a nonradioactive fragment of insulin or another chemical agent remains open.
Site of estrogen action in rabbit ovarian tissue
Authors: Holt J. A. , Dinerstein R. J. , Lorincz M. A.
Published: December 2017

In superovulated or naturally mated pseudopregnant rabbits, an abrupt premature decline of progesterone production by the corpus luteum occurs after removal of polydimethylsiloxane capsules filled with 17 beta-estradiol. Reinsertion of the estradiol-filled capsules stimulates a striking restoration of progesterone production. We have given [3H]estradiol by arterial infusion to anesthetized rabbits to determine by cellular autoradiography whether the exogenous estradiol localizes to luteal tissues responsible for progesterone production. Autoradiography with both freeze-dried and touch-thaw mounted preparations demonstrated that tritium activity localized to the nuclei of luteal cells and that such uptake could be blocked by radioinert diethylstilbestrol. We extracted the tritium activity sequestered in vivo by the corpora lutea and cocrystallized the extract with 14C-labeled and radiostable 17 beta-estradiol to confirm its presence (greater than 90%) as [3H]estradiol. In addition, we were able to demonstrate that radiostable diethylstilbestrol blocked ovarian uptake of 16 alpha-125I-17 beta-estradiol in vivo. In concert, these observations provide compelling evidence that the exogenous estradiol responsible for restoring progesterone production may act through an estrogen-specific mechanism directly in the luteal cells.
Affinity alteration of insulin receptor induced by a phorbol ester
Authors: Grunberger G. , Gorden P.
Published: December 2017

The effect of a phorbol ester tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA) on 125I-insulin binding to human cells was examined. TPA markedly inhibits insulin binding to cultured human lymphocytes and macrophages but has a minimal effect on human fibroblasts. This inhibition is temperature, time, and concentration dependent. The inhibition of insulin binding to the cells at 37 degrees C occurs within minutes and diminishes by 6 h of incubation. Insulin binding is decreased by TPA whether the phorbol ester is added before, after, or simultaneously with 125I-insulin to the cell suspension. Scatchard analysis of binding to IM-9 lymphocytes indicates that TPA affects the affinity rather than the number of insulin receptors. The phorbol ester has only a small effect on 125I-human growth hormone binding in cultured human lymphocytes. TPA perturbs the insulin receptor of cultured human lymphocytes in a fashion similar to its effect on the epidermal growth factor receptor of several other cell types. The specific mechanism of TPA action that affects the receptor of these two potent growth factors (i.e., insulin and epidermal growth factor), however, is unknown.
Pituitary blood flow
Authors: Page R. B.
Published: December 2017

The direction of pituitary blood flow, the amount of pituitary blood flow, its regional control, and the role of the median eminence microcirculation are the subjects of this review. Present concepts of pituitary blood flow are focused almost entirely on its direction and arouse from studies of pituitary vascular anatomy performed almost 50 years ago. The development of new anatomic techniques has led to a reappraisal of pituitary angioarchitecture, stimulated physiological studies to clarify the pattern of blood flow within the entire gland, and led to a reappraisal of accepted concepts of directional pituitary blood flow. The availability of techniques to accurately measure organ blood flow has permitted study of pituitary blood flow; and, when combined with knowledge of pituitary anatomy, the application of these techniques promises to provide a means to develop insight into control of the mechanisms by which chemical messengers are delivered to the pituitary to control its function. New anatomic techniques promise to develop new understanding of the three-dimensional arrangement of median eminence microvasculature and yield new concepts of blood flow regulation within the median eminence that can be tested by physiological means.
A possible mechanism of inotropic action of prolactin on rat heart
Authors: Karmazyn M. , Daly M. J. , Moffat M. P. , Dhalla N. S.
Published: December 2017

Prolactin possesses positive inotropic actions in isolated heart preparations although the mechanism of this influence is not understood. Our study was designed to investigate the mechanism of this effect on the rat heart. Prolactin (50 ng/ml) produced a time-dependent increase (60%) in contractile force that reached maximum after 30 min and remained steady for a further 30 min. A similar time-dependent phenomenon was seen with 200 ng/ml prolactin although the maximum inotropic effect was reduced. Indomethacin (30 micrograms/ml) significantly reduced the inotropic effect of both prolactin concentrations although the effect of the hormone was not related to the release of 6-keto-PGF1 alpha, the prostacyclin metabolite. Propranolol (1-20 micrograms/ml) significantly reduced the positive inotropic effect of prolactin. Prolactin however had no influence on myocardial adenylate cyclase activity. Hearts that were removed from animals pretreated with 1.25 or 2.50 mg/kg reserpine did not respond to prolactin administration. It is suggested that the inotropic influence of prolactin is mediated by endogenous catecholamine liberation.
Feedback inhibition by biosynthetic human insulin of insulin release in healthy human subjects
Authors: Waldhausl W. K. , Gasic S. , Bratusch-Marrain P. , Korn A. , Nowotny P.
Published: December 2017

To determine the impact of biosynthetic human insulin (BHI) on endogenous insulin release, splanchnic output and arterial concentrations of C-peptide were measured in eight healthy men after intravenous administration of 0, 0.5, 1.25, U BHI . m-2 . h-1 for 70 min each. Euglycemia was maintained by a variable glucose infusion. Arterial levels of serum insulin were 48 +/- 6 pmol/liter before and 135 +/- 12, 265 +/- 18, and 593 +/- 47 pmol/liter after BHI infusion. Splanchnic C-peptide output was reduced by BHI infusion from 88 +/- 10 pmol/min before to 50 +/- 9, 28 +/- 10, and 18 +/- 16 pmol/min (P less than 0.0025). Simultaneously, arterial concentrations of C-peptide fell from 539 +/- 54 pmol/liter by 29 and 43% when 1.25 and 2.5 U . m-2 . h-1 of BHI were administered. Hepatic insulin uptake was directly related with BHI infusion rate (r = 0.88) and rose during BHI administration from a basal value of 58 +/- 7 to an uptake of 265 +/- 31 pmol/min when 2.5 U . m-2 . h-1 were infused (P less than 0.0005). Basal hepatic insulin clearance was 4.75 +/- 0.60 ml . kg-1 . min-1 and remained unchanged after BHI infusion as did hepatic fractional extraction of insulin, which was 61 +/- 4% in the basal state. Metabolic clearance rate of immunoreactive insulin (MCRi) was dose-dependently reduced by BHI infusion, whereas the relative share of hepatic insulin clearance in total MCRi rose simultaneously (P less than 0.01). We conclude that feedback inhibition of endogenous insulin release may play an important role in vivo. Furthermore, it appears that nonhepatic insulin degradation is a saturable phenomenon as total MCRi fell in the presence of its unchanged hepatic clearance rate after the infusion of large amounts of BHI.
Glucocorticoid-induced atrophy is not due to impaired excitability of rat muscle
Authors: Ruff R. L. , Martyn D. , Gordon A. M.
Published: December 2017

We explored the possibility that glucocorticoid-induced muscle weakness and atrophy resulted from impaired muscle membrane excitability. Male Sprague-Dawley rats received intramuscular injections of dexamethasone, cortisone acetate (equivalent anti-inflammatory doses), or saline for up to 28 days. Temporal patterns of change in muscle mass, twitch and tetanic tension, and membrane potential, cable parameters, and excitability were studied in vitro in the extensor digitorum longus (EDL), soleus (SOL), omohyoid (OMO), caudofemoralis (CF), and the sternomastoid muscles (membrane potential only). the membrane properties of EDL fibers were also studied in vivo (pentobarbital anesthesia). The relative severity of atrophy was OMO greater than CF greater than EDL greater than SOL. Reduction in twitch or tetanic tension never preceded atrophy. The twitch and tetanic tension (per g muscle) increased with glucocorticoid treatment. There were no significant changes in the time course of the twitch or tetanus. Dexamethasone produced more severe atrophy and force reduction than did cortisone acetate. Glucocorticoid treatment produced a depolarization of EDL muscle fibers measured in vitro at 23 degrees C, but this did not appear to be physiologically significant because EDL fibers studied in vivo were not depolarized and had normal action potential amplitudes and thresholds. Glucocorticoid treatment did not change the membrane resistance or capacitance. We conclude that glucocorticoid treatment did not produce muscle weakness by impairing sarcolemmal excitability or excitation-contraction coupling, but that the weakness resulted from muscle atrophy.
Effect of physical training on transport and metabolism of glucose in adipocytes
Authors: Vinten J. , Galbo H.
Published: December 2017

Adipocytes were prepared from the epididymal fat pads of rats trained by swimming (T) and from control rats matching the T rats with respect to free-feeding and age (FC), body weight and age (WC), or mean fat cell size and age (CC). The number of epididymal fat cells was the same in all groups, whereas the mean adipocyte volumes (in pl) differed (P less than 0.01): 153 (T and CC), 266 (WC), and 540 (FC). The initial influx rate of 3-O-[14C]methylglucose (60 mumol/liter) in maximally insulin-stimulated adipocytes was more than twofold higher in T rats than in any control group (P less than 0.01). In the control groups, influx was positively correlated to cell size. Also the maximally insulin-stimulated incorporation of 14C from [U-14C]glucose into lipids was significantly higher in T rats than in the control groups. The saturable binding of mono[125I-TyrA14]insulin was about 18% higher in T rats than in WC rats in the insulin concentration range from 30 to 20 X 10(4) pmol/liter. In conclusion, physical training markedly increases 3-O-methylglucose transport in fat cells, an effect that cannot be elicited by reduction in body weight or fat cell size.
Comparison between K+-induced and LHRH-induced gonadotropin secretion in vitro
Authors: Turgeon J. L. , Waring D. W.
Published: December 2017

The effect of elevated external [K+] compared to luteinizing hormone-releasing hormone (LHRH) on gonadotropin secretion was studied in vitro in superfused pituitary fragments from cyclic female rats. Challenging proestrous but not estrous pituitaries with a 2-h pulse of 0.8 nM LHRH produces two distinct peaks in the curve for the first derivative of gonadotropin secretion versus time; the second peak exceeds the initial one and represents expression of LHRH self-priming. Challenging proestrous pituitaries with a 2-h pulse of raised [K+] results in an initial increase in secretion followed by a positive slope of the secretion rate curve for LH but a constant rate for follicle-stimulating hormone (FSH); the positive slope is blocked by cycloheximide and not found with estrous pituitaries pulsed with raised [K+]. Proestrous pituitaries exhibit a graded response to 10-min pulses of raised external [K+] from 10-91 mM for LH and 10-47 mM for FSH secretion. LHRH followed by elevated [K+] primed the LH and FSH response to the secretagogue, but the reverse sequence did not. The results show 1) a concentration dependence of elevated [K+]-induced LH and FSH secretion, 2) a LHRH specific initiation of priming that does not require the immediate presence of LHRH for its subsequent expression, and 3) a gonadotropin secretory response to elevated [K+] that varies during the estrous cycle and can be modified by protein synthesis inhibition or progesterone administration.
Direct antigonadal activity of cannabinoids: suppression of rat granulosa cell functions
Authors: Adashi E. Y. , Jones P. B. , Hsueh A. J.
Published: December 2017

The direct effects of delta 9-tetrahydrocannabinol (THC) and related cannabinoids on ovarian granulosa cells were studied in vitro. Granulosa cells from immature, hypophysectomized, estrogen-treated rats were cultured for 2 days in an androstenedione-supplemented medium in the presence or absence of follicle-stimulating hormone (FSH) (10 ng/ml) with or without cannabinoids. FSH treatment increased progesterone and estrogen biosynthesis, whereas concomitant treatment with THC led to a dose-dependent inhibition of the FSH-stimulated accumulation of progesterone and estrogen with ED50 values of 3.5 +/- 0.3 X 10(-7) and 1.8 +/- 0.2 X 10(-6) M, respectively. Treatment with related but nonpsychoactive cannabinoids (cannabidiol, cannabinol, cannabigerol, or cannabichromene) was equally effective. The THC-induced inhibition of progesterone production was reversible and was associated with an inhibition of pregnenolone biosynthesis and a decrease of 3 beta-hydroxysteroid dehydrogenase activity. In addition, treatment with THC brought about a dose-dependent inhibition of the FSH-induced increase in luteinizing hormone (LH) receptors. The inhibitory effects of THC were not associated with changes in cell number, protein content, or cell viability. Thus, THC exerts direct inhibitory effects on FSH-dependent functions related to steroidogenesis and the acquisition of LH receptors, all of which are essential to follicular maturation. Because plasma concentrations of THC similar to those used in this study have been reported in human beings, repeated exposure of female users to THC may lead to ovarian dysfunction, due in part, to the direct antigonadal activity to THC.