Development of differential sperm tail swelling patterns during exposure of human spermatozoa to hypoosmotic environments regulated by a colloid osmotic pressure effect

The colloid osmotic pressure effect, generated by the incorporation of proteins, on the tail swelling response of human spermatozoa under hypoosmotic conditions has been recently evaluated (CorreaPérez et al., 2003). The findings of that study suggested that the supplementation of hypoosmotic media with a protein source delayed intracellular water uptake (Correa-Pérez et al., 2003). Thus, under those conditions, the onset and transition of the sperm tail swelling response can be observed in a controlled manner, as it does not occur abruptly as in conventional hypoosmotic solutions without protein supplementation. The objective of this study was to evaluate the swelling behaviour of the sperm during the initial exposure and continued incubation in a hypoosmotic environment regulated by the colloid osmotic pressure effect. Normozoospermic semen specimens (n 1⁄4 20) were obtained and processed to select a highly motile sperm population before exposure to the hypoosmotic solutions, as previously described (Correa-Pérez et al., 2003). Two hypoosmotic solutions were prepared to induce the sperm swelling response. The first solution, referred as hypoosmotic swelling solution (HOS), was prepared by mixing equal volumes of fructose–sodium citrate solutions and adjusted to an osmotic pressure of 150 mOsm l. The second solution, referred as hypoosmotic synthetic serum substitute (H-SSS), was prepared by diluting serum substitute supplement (SSS; Irvine Scientific, Santa Ana, CA, USA) with distilled water and adjusted to an osmotic pressure of 150 mOsm l. Aliquots of the processed spermatozoa were added 1 : 10 (v/v) to each of the hypoosmotic solutions and incubated for 30 min at 37 C. The sperm’s response to the hypoosmotic environments was assessed immediately after exposure (0 min), at 1-min intervals for the first 5 min of incubation, and at 5-min intervals from 5 to 30 min of incubation. Specimens were evaluated on wet mount preparations for percentage of total and specific tail swelling patterns (Correa-Pérez et al., 2003). Specific swelling patterns were defined as those exhibited by sperm undergoing maximal tail swelling (>50% tail length swelling; main-piece to neck-piece) or minimal tail swelling (<50% tail length swelling; end-piece to main-piece). Swelling patterns could be observed with or without associated motility. A control sample (processed sperm only) was also assessed at the same intervals for percentage of sperm motility and spontaneous sperm swelling. Differences between sample means were evaluated by Student’s t-test. Statistical significance was considered at a level of P < 0.05. The total swelling of spermatozoa exposed to the HOS solution ranged from 62.0 ± 4.9% to 71.0 ± 3.0% during incubation (Fig. 1; P < 0.05). The predominant tail swelling patterns developed during the incubation period were maximal swelling/immotile and minimal swelling/immotile (Fig. 1). Immediately following exposure of sperm to the HOS solution, approximately 37.5 ± 6.2% of spermatozoa exhibited the maximal swelling/ immotile pattern. The proportion of this swelling pattern increased rapidly during the first 2 min of incubation, and tended to continue increasing until the end of the incubation period (54.0 ± 8.1%). The minimal swelling/immotile pattern reacted with approximately 21.0 ± 8.1% swelling immediately after exposure to the HOS solution Correspondence: Juan R. Correa-Pérez, PhD, Centro de Fertilidad del Caribe, Torre San Francisco Suite 606, 369 Ave De Diego, Rı́o Piedras, Puerto Rico 00923. Tel. /Fax: 787-7632773; E-mail: dr_jrcorrea@hotmail.com andrologia 36, 84–86 (2004) Accepted: February 19, 2004