Ronald M. Hoskinson

Modification of Sheep Pineal β-Adrenoceptors by Some Gonadal Steroids but Not by Melatonin

The effects of active immunization against a range of gonadal steroids on pineal beta-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 beta-adrenoceptor density or ligand binding affinity. Immunization against estrone or 17 beta-estradiol significantly increased binding affinity and decreased beta-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 beta-receptor density and an increase in binding affinity were noted in the ovariectomized animals. Androstenedione-releasing implants decreased beta-receptor density and increased beta-receptor affinity in pineals from intact ewes, but these implants had no effect on pineal parameters in ovariectomized ewes. Immunization of ewes against 17 beta-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 beta-receptors in ewes, while specific androgens may act indirectly on these receptors to modify their interaction with estrogens.

Effects of steroids on β-adrenergic binding sites in sheep pineal glands

Abstract As an initial step in investigations of putative differences between central nervous system light-sensitive mechanisms in seasonally shedding and non-shedding breeds of sheep, some β-adrenoceptor characteristics of Merino sheep pineal glands were determined, using [ 3 H]dihydroalprenolol as the labelled ligand. Overall, a dissociation constant of 17.2 ± 2.6 moles/I and a daytime β-receptor density of 1.6 ± 0.3 pmoles/mg were determined at 37°. The binding sites exhibited stereospecificity, saturability and apparent homogeneity. 17β-Estradiol and progesterone implants that provided hormone concentrations in the physiological range had no significant effect on pineal β-receptors in male sheep castrated shortly after birth. Dexamethasone injections, on the other hand, in doses sufficient to loosen the attachment of wool fibres to the skin, resulted in decreased pineal β-receptor density and increased receptor affinity for dihydroalprenolol. This effect was apparently not mediated by altered plasma catecholamine concentrations, since the glucocorticoid treatment did not affect jugular venous noradrenaline, adrenaline or dopamine levels. The possible involvement of glucocorticoids in the regulation of wool growth could thus have a central neuronal component, mediated via action on pineal β-adrenoceptors in sheep; however, the existence of the putative gonadal steroid feedback on β-adrenoceptor-mediated pineal function remains to be demonstrated in this species.

Seasonal Changes in the Sensitivity of Ovine Pineal β- Adrenoceptors to Steroids

Immunoneutralization of endogenous gonadal steroids has recently been shown to modify pineal β-adrenoceptor function in intact Merino ewes. In the current study, interactions between gonadal steroids

Effect of Immunization Against Melatonin On Seasonal Fleece Growth in Feral Goats

Abstract: Four vaccination protocols were utilized to investigate the effects of immunoneutralizing circulating melatonin on the annual cashmere growth cycle and cashmere production in Australian feral goats. A fluctuating anti‐melatonin antibody response, achieved by repeated booster vaccinations, resulted in an acceleration of the growth cycle in goats which exhibited a significant immune response, compared to sham‐immunized controls. Responding goats showed two cycles of cashmere length growth in the first 16 months and increased annual cashmere production in the first year. However, in the second year, these effects were no longer apparent, suggesting either some form of desensitization to melatonin, or a diminished response due to declining antibody titre. The effects of immunization were observed in both sexes; the effect on cashmere length was greater in wethers than in does. Cashmere fibre growth in response to a continuously declining plane of specific antibody showed increased cycle frequency, albeit with a decreased amplitude; guard hair growth cycles were affected to a much lesser extent. Small transient peaks of specific immunity at the summer or winter solstice were without significant effect on cashmere growth. Immunization to provoke a persistent anti‐melatonin antibody response at the winter solstice resulted in significantly increased greasy fleece weight, % cashmere yield, and mass of cashmere produced, but no change in fibre diameter in both sexes. Thus the timing of cashmere growth cycles in goats may be, at least transiently, altered by appropriately timed immunization against melatonin. The mechanism of pineal‐mediated regulation of cashmere growth cycles may involve (i) entrainment of an endogenous rhythm by melatonin, or (ii) seasonal alteration of cashmere follicle sensitivity to the effect of melatonin.

Enzyme Inhibition by Tobacco Smoke: A Comparison of the Effects of Four Filters

The effects of four types of cigarette filters on the inhibition of glyceraldehyde-3-phosphate dehydrogenase by aqueous solutions of the free gas phase of tobacco smoke have been studied. Commercial cellulose acetate-charcoal filters or experimental wool filters containing a polyethyleneimine-quaternary ammonium additive were particularly effective in removing the inhibitor(s) from smoke under prescribed experimental conditions. Inhibition was dependent in all cases on both the age and the amount of free gas phase solution as well as contact time. Transient enzyme activation was observed. It is suggested that hydrogen sulfide is the main inhibitor present in the gas phase of cigarette smoke.

Response of pineal β-adrenoceptors in different breeds of sheep to immunization against selected steroids

Active immunization of Merino and Wiltshire Horn X Merino cross-bred sheep against a range of gonadal steroids has revealed that pineal beta-adrenoceptors in both breeds are sensitive to hormonal modification by androgens, but only in the less seasonal, non-shedding Merino do these receptors appear to be sensitive to regulation by estrogens. Neither breed showed sensitivity of its pineal beta-adrenoceptors to active immunization against the pineal hormone melatonin under either normal or reversed photoperiod treatment. These results (a) suggest that pineal related seasonal differences between the breeds (i.e. wool shedding and/or reproductive function) may reside in differential sensitivity of the pineal gland to regulation by specific circulating steroid hormones, and (b) indicate an absence of end-product regulation of beta-adrenoceptor-mediated pineal melatonin biosynthesis in both seasonally shedding and non-shedding sheep.