Plasma Prolactin Levels in Maturing Intact and Cryptorchid Male Rats: Development of Stress Response

In order to determine the possible role of the seminiferous tubules in the regulation of prolactin secretion during sexual development, male rats were rendered cryptorchid at 22 days of age, and thereafter different groups of animals were decapitated at 8-10 day intervals between Day 32 and Day 70. Cryptorchid rats showed destruction of the germinal epithelium accompanied by increased plasma FSH and, to a much lesser extent, increased plasma LH titers. Nevertheless, plasma prolactin levels were similar to those of intact controls throughout the entire period studied. Plasma prolactin titers in intact controls remained uniformly low from Day 20 to Day 70, contrasting with previous reports in which increasing prolactin levels have been observed during sexual development. To determine the reason for this apparent discrepancy, a longitudinal experiment was conducted in which intact and cryptorchid male rats were bled every 10 days from Day 30 to Day 70, following a 3-min period of exposure to ether fumes. The prolactin response to this stress increased markedly with age. A similar pattern of prolactin was observed in a cross-sectional study in which different groups of intact animals were bled following a 3-min period of ether exposure, at ages ranging from 20 to 70 days. The results indicate that unlike FSH secretion, prolactin secretion is not controlled by the seminiferous tubules. In addition, they suggest that the pattern of increasing plasma prolactin previously described in the developing male rat is at least in part caused by an age-dependent increase in responsiveness of prolactin to stress. The authors wish to thank Miss Cheri Reimann for secretarial assistance.