EFFECTS OF BROMOCRIPTINE-INDUCED HYPOPROLACTINAEMIA ON GONADOTROPIN-SECRETION AND TESTICULAR FUNCTION IN RAMS (OVIS-ARIES) DURING 2 SEASONS

The influence of low circulating concentrations of prolactin on gonado trophin and testosterone secretion, sperm production and testicular gr owth was investigated in rams during two different seasons. Treatment of Dorset rams (n = 23) with bromocriptine (4 mg day(-1)) during the s pring (n = 11) and autumn (n = 12) caused a significant decrease in ba sal, mean and total serum prolactin concentrations (P < 0.01). In spri ng, serum prolactin concentrations returned to pretreatment values, on e week after the termination of treatment. Basal, mean and total serum concentrations of LH were significantly higher in treated rams than i n controls during the treatment period in autumn (P < 0.05). Secretion of LH was not affected by bromocriptine treatment during spring. Ther e were no differences in the secretion of FSH between treated and cont rol rams in either season. Serum concentrations of testosterone were s ignificantly lower in treated rams than in control rams during the tre atment period in autumn (P < 0.05) but not during spring. Semen volume from treated rams was significantly lower during the period after tre atment in autumn (P < 0.05). Scrotal circumference decreased during bo th seasons in treated animals, but this change in size was significant only during spring (P < 0.05). Conversely, there was an increase in s crotal circumference in control rams during both seasons. It is conclu ded that prolactin may (i) affect LH secretion and, (ii) influence tes ticular function in rams, by directly affecting testosterone and semen production during autumn, and retarding testicular growth in spring.