Dopaminergic inhibition of gonadotropic release in hibernating frogs, Rana temporaria.
The influence of a dopaminergic antagonist, metoclopramide (MET), and an agonist, bromocriptine (BROMO), on reproductive status was examined in female frogs, Rana temporaria. MET induced advanced ovulation during hibernation, suggesting dopaminergic inhibition of gonadotropin (LH) release during this period. BROMO did not decrease plasma LH in intact females in comparison with vehicle (VEH)-treated controls (VEH: 11 +/- 6 vs BROMO: 5 +/- 4 ng/ml) or in sham-lesioned (SL) females (SL; 12 +/- 5 vs SL + BROMO: 9 +/- 8 ng/ml). However, BROMO significantly depressed the rise in plasma LH following lesioning (L) which disconnected the hypothalamus from the medium eminence-pituitary complex (L + BROMO: 29 +/- 10 vs L: 74 +/- 30 ng/ml; P < 0.002). Taken together with previous results of lesion studies, these data point to an important role of dopaminergic inhibition in the regulation of seasonal reproduction in this frog.