Capacity of individual somatotropes to release growth hormone varies according to sex: analysis by reverse hemolytic plaque assay.
A reverse hemolytic plaque assay was used to investigate the mechanism(s) underlying sexual differences in GH release which evolve at puberty in rats. The percentages of GH-secreting cells in 24-h pituitary cultures from each sex were similar for pituitary donors up to 30 days of age (range = 38.9% to 41.7% of all cells in culture, n = 3 separate experiments) but decreased by day 50. The decrease was more striking for females (to 24.1 +/- 0.3% mean +/- SE) than for males (to 33.2 +/- 1.1%). However, owing to the greater increase in total pituitary cell number exhibited by female rats at this time, the absolute numbers of somatotropes recovered from male and female pituitaries were almost identical on 50 and 100 days of age. To assess the secretory capacities of individual somatotropes, we measured the sizes of plaques formed. In prepubertal rats (days 10-30), the plaque areas under basal conditions were comparable for males and females at each age studied, and treatment with GH-releasing factor increased plaque sizes to approximately the same degree (10-fold) for both sexes at each age. However, by day 100, plaques that formed under both basal and stimulated conditions were consistently larger (P less than 0.01) for male than for female donors. Taken together, our results demonstrate that sexual differences in GH release are attributable to the secretory capacities of individual somatotropes rather than to differences in the numbers of GH cells in pituitaries of male and female rats.
D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006462:Hemolytic Plaque Technique; D008297:Male; D008722:Methods; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D012727:Sex Characteristics; D012741:Sexual Maturation
D013006:Growth Hormone