Melanocyte-stimulating activity in the pituitary, blood plasma and amniotic fluid of the fetal guinea pig
Creators: name: Bryant, Harold Norman William
Publisher: name: University of British Columbia
Year: 2010

description: Melanocyte-stimulating activities were measured in the fetal guinea pig in order to determine whether melanocyte-stimulating hormone (MSH) was present over the latter half of gestation. Activity was measured by bioassay using skin of the lizard, Anolis carolinensis, in vitro. The ability of unknown samples to darken the skin was measured in equivalent amounts of synthetic alpha-MSH. Pituitary activity was measured in both the posterior and anterior lobes in fetuses from 39 to 70 days of gestation. Posterior pituitary values ranged from 18.0 ng/lobe at 39 days to 108l ng/lobe at 70 days and from 288 ng/mg at 39 days to 2962 ng/mg at 70 days. Anterior lobe activity ranged from 10.5 ng/lobe at 42 days to 403 ng/lobe at 70 days and from 42.4 ng/ mg at 55 days to 523 ng/mg at 70 days. Whole pituitary activity ranged from 28.9 ng/gland at 39 days to 1484 ng/gland at 70 days and from 143 ng/mg at 55 days to 1308 ng/mg at 70 days. In all cases, there was a clear linear relationship between age in days and the log of the measured activity both in ng/gland and in ng/mg. The average ratio of posterior lobe to anterior lobe activity was 3-0 (per lobe) or 6.7 (per weight). Activity in a litter of newborns agreed closely with activities in fetuses of the same post-coitum age. The average pituitary activity in four adults was 8620 ± 1300 ng/gland or 2600 ± 590 ng/mg (mean ± standard error of the mean). Activity in fetal brain tissue was 1.36 ± 0.24 ng/mg and in one sample of adult brain tissue was 0.75 ng/mg. Melanocyte-stimulating activity was measured in 13 pooled samples of fetal plasma. Age ranged from 45 to 70 days of gestation. Average plasma activity was 10.0 ±1.6 ng/ml and activity did not appear to change with increasing gestational age. Activity in the plasma in four out of five pregnant guinea pigs was 12.1 ± 2.8 ng/ml. In the fifth animal no measurable activity was present. Activity in normal adult females was 7.9 ± 2.2 ng/ml. There was no significant difference between the activity in the two adult groups (Student's t test, unpaired observations, variances equal). There was also no significant difference between either adult group and the plasma activity In the fetus. Plasma activity in newborns was 1.92 ± 0.63 ng/ml. Thus an apparent drop in activity occurs just after birth. However, the activity was only significantly different from levels in either adults or the fetus at P&lt;0.1. Amniotic fluid melanocyte-stimulating activity was measured in 30 samples taken from fetuses ranging in age from 42 to 67 days of gestation. Activity was detected in 10 samples, but was only measurable in eight. Activity was 79.4 ± 14.3 pg/ml. No changes occurred with increasing gestational age. Incubation of samples with trypsin indicated that a protein was involved. Fourteen other amniotic fluid samples had a lightening effect on the Anolis skin. The substance responsible for this activity was not identified. Melanocyte-stimulating activity is found in high levels in the guinea pig fetus. This study provides the first comprehensive measurement of the dynamics of melanocyte-stimulating activity in the fetus over the latter part of gestation in both the pituitary and the plasma. Activity is also present in newborns and in adults. Identification of specific peptides must await further study. This study supports evidence collected in other species that MSH or related peptides may be important in fetal physiology and/or pregnancy in mammals.