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P. J. Battista and W. A. Condon

Summary. Incubation of bovine luteal cells with the alternative pathway catecholamines octopamine, synephrine and deoxyadrenaline at concentrations of 10 −6 to 10−3 m enhanced the production of progesterone (P < 0·05). Tryamine did not alter basal progesterone production (P > 0·05). Addition of noradrenaline and adrenaline at concentrations of 10−4 to 10−7 m significantly elevated the production of progesterone (P < 0·05). The steroidogenic response to noradrenaline and adrenaline was greater than that for octopamine, synephrine and deoxyadrenaline (P < 0·05). Response to both primary (10−6 m) and alternative (10−4 m) pathway catecholamines was inhibited by propranolol (10−5 m, P < 0·05) but not phentolamine (10−5 m, P > 0·05). These results demonstrate that octopamine, synephrine and deoxyadrenaline can affect steroidogenesis by bovine luteal cells, and their action is mediated by β-adrenergic receptors.

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P. J. Battista and W. A. Condon

Summary. The addition of acetylcholine or histamine (10− 7 to 10−4 m), γ-aminobutyric acid, a dopamine agonist, and melatonin (10−7 to 10−5 m) did not alter basal or LH-stimulated progesterone production (P>0.05). The addition of the specific β2-adrenergic agonist terbutaline and salbutamol did not significantly elevate progesterone production. Treatment of luteal cells with serotonin (5-HT), 10−6 to 10−4 m, increased the production of progesterone (P<0.05). This stimulated production was inhibited by the addition of mianserin (10−5 m, a 5-HT antagonist; P<0.05). Isoproterenol (10−7 to (10−4 m) also resulted in significant increases in progesterone production (P<0.05). The combined treatments of 5-HT + LH, isoproterenol+ LH, or isoproterenol + 5-HT did not result in a further increase in progesterone above that observed in response to LH or isoproterenol alone (P>0.05). The isoproterenol-induced progesterone production could not be blocked by butoxamine (10−5 m, a β2-antagonist), or practolol (10−5 m, a β1-antagonist), but was inhibited by propranolol (10−5 m, a general β-antagonist; P<0.05). The response to isoproterenol was unaffected by mianserin (10−5 m). These results demonstrate a possible role for 5-HT in the regulation of steroidogenesis by the corpus luteum of the cow. Furthermore, these results suggest that serotonin-induced progesterone production is a receptor-mediated event.

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P. J. Battista, J. P. Poff, D. R. Deaver, and W. A. Condon

Summary. Biogenic amines were administered using osmotic pumps placed subcutaneously in the neck region of regularly cycling, non-lactating dairy cows on Days 9–11 (oestrus = Day 0) of the oestrous cycle. Blood samples were collected using indwelling jugular catheters and the plasma progesterone concentrations were measured. Samples were collected at 4-h intervals for the first 12 h of treatment and thereafter at 12-h intervals for the remainder of the 72-h treatment period. After administration of various doses of noradrenalne, adrenaline and serotonin (0·5–2·0 μg/kg/h) significant elevation of plasma progesterone was achieved at a dosage of 2·0 μg/kg/h (P < 0·01). The response to adrenaline was greater than that observed for noradrenaline and serotonin (P < 0·05). Within-treatment comparison to pretreatment samples showed plasma progesterone concentrations to increase within 4 h after the administration of noradrenaline, adrenaline and serotonin (P < 0·05) and this enhancement was maintained throughout the treatment period (P < 0·05). The elevation in plasma progesterone concentrations induced by noradrenaline, adrenaline and serotonin was independent of changes in circulating concentrations of luteinizing hormone. These results support a physiological role for endogenous biogenic amines in the control of bovine luteal progesterone production.