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Effect of cold and hot ambient temperatures on plasma progesterone concentrations in ewes with intact and denervated ovaries containing experimentally maintained corpora lutea

Summary. Twenty ewes in which maintained corpora lutea had been established were subject to 1 of 3 treatments: denervation of the ovaries by freezing, denervation of the ovaries using the chemical 6-hydroxydopamine, or control. The animals were exposed sequentially to normal (24·5°C), cold (10·7°C), normal (23·8°C), hot (39·4°C) and normal (24·6°C) temperatures, each for 1 week. On the final 3 days of exposure rectal temperatures and heart rates were measured, and on the final day the body weights, respiratory rates, and blood glucose concentrations were measured and a series of 5 blood samples was collected from each ewe for determination of the progesterone concentrations. The progesterone concentration was greatest during the hot period in 8 of the 12 animals, particularly in the ewes with denervated ovaries (6 of the 7 animals). This suggests that high ambient temperatures increase progesterone concentrations non-specifically, and that denervated ovaries are more sensitive to the circulating catecholamines that presumably mediate this effect. The progesterone concentrations were lower (P < 0·001) in the groups with freezing or chemically denervated ovaries (2·86 and 2·73 ng/ml respectively) than in the control group (3·38 ng/ml), suggesting that the ovarian innervation plays a physiological role in regulating progesterone secretion.

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