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The effects of active immunization against a range of gonadal steroids on pineal β-adrenoceptors were studied in cycling Merino ewes. In selected cases, the effects of exogenous steroids were also investigated. Immunization against progesterone had no detectable effect on pineal β-adrenoceptor density or ligand binding affinity. Immunization against estrone or 17β-estradiol significantly increased binding affinity and decreased β-receptor density. Testosterone immunization in ewes caused similar effects but to a lesser degree. In contrast, immunization against androstenedione resulted in a decreased affinity and an increase in receptor density in ewes. In subsequent experiments, some parameters of pineal function in intact cycling and ovariectomized ewes were compared; a significant decrease in β-receptor density and an increase in binding affinity were noted in the ovariectomized animals. Androstenedione-releasing implants decreased β-receptor density and increased β-receptor affinity in pineals from intact ewes, but these implants had no effect on pineal parameters in ovariectomized ewes. Immunization of ewes against 17β-estradiol had no significant effects on basal or isoprenaline-stimulated N-acetyltransferase or adenyl cyclase activities. Immunization of ewes against melatonin, or in vitro incubation of pineal glands with the hormone had no effects on the pineal parameters studied. It is concluded that estrogens affect the pinealocyte β-receptors in ewes, while specific androgens may act indirectly on these receptors to modify their interaction with estrogens.

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