Reductions in plasma LH concentration and testicular weight in ring doves following intracranial injection of prolactin or growth hormone.

Testicular weights and concentrations of LH in plasma were measured in individually housed adult male ring doves given five daily intracerebroventricular injections of saline-NaHCO3 vehicle (2 microliter), ovine prolactin (0.1, 0.5, 1.0 or 2.0 micrograms/day), turkey prolactin (1.0 micrograms/day), turkey GH (1.0 micrograms/day) or ovine GH (1.0 micrograms/day). Administration of ovine prolactin resulted in a dose-dependent suppression of plasma LH concentration, with values in the two highest dose groups averaging three- to fivefold less than those of vehicle-injected controls. Reductions of similar magnitude were obtained following intracranial administration of turkey, ovine or human GH. Whilst effective in reducing plasma LH, turkey prolactin was less effective than an equivalent dose of ovine prolactin. Testicular regression was observed in all treatment groups which showed a significant decrease in plasma LH concentrations. Because crop sacs remained undeveloped in all treatment groups, it was concluded that these centrally administered hormones acted primarily at the level of the brain or pituitary to exert their suppressive effects. The possibility that prolactin and GH interact with different binding sites to inhibit LH secretion is discussed, together with evidence for a possible role of prolactin and GH in gonadotrophin regulation under normal physiological conditions.