Effects of Chronic Hyperprolactinemia on Sexual Arousal and Erectile Function in Male Rats

Abstract

Studies were conducted to determine if the inhibitory effects of chronic hyperprolactinemia on sexual behavior in male rats occur through reduced sexual arousal as opposed to reduced erectile function. Pituitary-grafted (hyperprolactinemic) and sham-operated, gonadally intact male rats were given standard tests of copulatory behavior, mounting behavior tests after genital anesthetization and penile reflex tests while restrained in a supine position. Beginning 7 days after pituitary transplantation, the number of erections displayed in penile reflex tests was significantly reduced in the pituitary-grafted animals. Increased intromission latencies and reduced intromission rates in tests of copulatory behavior were also observed at this time. Beginning 3–4 weeks after surgery, mounting rates were inhibited in hyperprolactinemic animals in both the copulatory behavior tests and tests of mounting behavior after genital anesthetization. Prolactin levels were significantly elevated in the pituitary-grafted animals, but serum testosterone levels were unaffected. To determine if the effects of hyperprolactinemia on erectile function occurred through changes in supraspinal input to neurons in the spinal cord controlling erectile function, pituitary-grafted and sham-operated male rats were subjected to spinal transection (between vertebral levels T6 and T9). Beginning 7 days later, penile reflex performance was re-examined. Hyperprolactinemic animals displayed significantly fewer erections during the initial test, but not in tests performed 10 and 13 days after spinal transection. The pituitary-grafted animals also showed a significant reduction in latency to the first erection with each successive test, suggesting a delayed recovery from increased supraspinal inhibitory input. These results show that hyperprolactinemia inhibits both sexual arousal and erectile function, and suggest that the inhibition of erectile function occurs through an effect of the hyperprolactinemic state at a supraspinal level within the central nervous system.

Pharmacological analysis of male rat sexual behavior

“…Likewise, a significant reduction in the number of penile flips was observed in ex copula supine tests [79]; such penile flips appear to facilitate vaginal mtromission [ 112,191 ] The inhibitory effects of elevated PRL levels on erectile potency appear to be medmted by central nervous tissue [79]. The suppression of penile reflexes in hyperPRL was reversed after transection of the spinal cord.…”

“…The induction of hyperPRL by injection of minced PRL secreting tumors resulted m a significant suppression of penile erections ehcited in a supine test beginning 34 days after tumor inoculation [58]. In contrast, hyperPRL was found to decrease the number of erections as early as 7 days after pttmtary transplant [79]. The differences in the animals' sensitivity to hyperPRL's effect on erectile function may be straindependent.…”

“…Prolactin (PRL) ~s an anterior p~tmtary hormone that has many effects on male reproductive organs and copulatory behavior Short-term exposure (5 days or less) to elevated PRL levels has been shown to enhance sexual arousal by decreasing mount and introm~ssion latencies [82] However, long-term exposure has been found to depress both sexual arousal and potency of men [23,181,200] and male rats ( [27,58,79] reviewed in [81]) The existence of PRL-containmg neurons m hypothalam~c areas important in the regulation of male copulatory behavior [95,218], and the possibility of the retrograde transport of PRL from the pituitary to the brain via the hypophyseal portal system [34] suggest that PRL may act directly on hypothalamic tissue to produce its effects on sexual behavior.…”

“…Two recent studies [58,79] have sought to determine whether deficits in sexual arousal or in potency are related to hyperPRL-induced impairment of copulatory behavior. The induction of hyperPRL by injection of minced PRL secreting tumors resulted m a significant suppression of penile erections ehcited in a supine test beginning 34 days after tumor inoculation [58].…”

“…The suppression of penile reflexes in hyperPRL was reversed after transection of the spinal cord. Therefore, the inhibition of penile reflexes observed in hyperPRL animals may be exerted by as yet unidentified supraspmal site(s) [79] Sexual motivation was also inhibited in hyperPRL animals; mounting rates after penile anesthetlzat~on were significantly reduced, although this effect first appeared 28 days after pituitary transplantation (as compared to the deficits in erectile responses noted in these ammals 7 days after transplantation) [79]. Thus, the results suggest that deficits in sexual motivation may be secondary to a deficit in erectile function.…”