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

Abstract

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\ m=. \ 5\ s=deg\ C), cold (10\ m=. \ 7\ s=deg\ C), normal (23\ m=. \ 8\ s=deg\ C), hot (39\ m=. \ 4\ s=deg\ C) and normal (24\m=.\6\s=deg\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\m=.\001) in the groups with freezing or chemically denervated ovaries (2\m=.\86 and 2\m=.\73 ng/ml respectively) than in the control group (3\m=.\38ng/ml), suggesting that the ovarian innervation plays a physiological role in regulating progesterone secretion.

Influence of adrenergic receptors on ovarian progesterone secretion in the pseudopregnant cat and oestradiol secretion in the oestrous cat

“…Since propranolol has no direct action, and works rather by blocking the adrenergic receptor from stimu¬ lation by the endogenous neurotransmitter or administered agonists, the reduction in the pro¬ gesterone secretion rate in response to propranolol described here suggests that the measured pre-infusion secretion rate was itself the consequence of endogenous, physiological adrenergic stimulation. This agrees with the earlier observation of decreased peripheral progesterone concen¬ trations in sheep with denervated ovaries (Wheeler & Blackshaw, 1986). Presumably therefore, variation in the activity of the autonomie sympathetic nervous system has an effect similar to that produced by the drugs used here, increasing sympathetic tone increasing adrenergic neurotrans¬ mitter (principally noradrenaline) and adrenal medulla hormone (principally adrenaline) release and consequently ovarian progesterone secretion.…”

“…The antiserum ( 11P27; Fanti & Wang, 1984) had cross-reactions of 100% with proges¬ terone, 96% with 1 la-hydroxyprogesterone, 11 % with 5a-pregnane-3,20-dione, 4% with 6ß-hydroxyprogesterone, 1 % with pregnenolone, and < 1 % with 20ß-dihydroprogesterone, 17-hydroxyprogesterone and androstenedione; no other steroid cross-reacted at >0T%. The progesterone radioimmunoassay method has been described elsewhere (Wheeler & Blackshaw, 1986). The efficiency of extraction was 80-6 ± 2-28% (n = 38).…”

“…The oestradiol immunoassay was conducted as described for progesterone (Wheeler & Blackshaw, 1986) with the following differences: 200 pi aliquants of plasma were extracted with 2 ml diethyl ether, the standards ranged from 1 to lOOOpg/tube (oestradiol-17ß; Sigma) and the radioactive label was [2,4,6,7-3H]oestradiol (Amersham International, Sydney, N.S.W. ; 3-37 TBq/mmol).…”

Different Effects of Subnormal Levels of Progesterone on the Pulsatile and Surge Mode Secretion of Luteinizing Hormone in Ovariectomized Goats1

“…Some reports have suggested that the plasma concentration of progesterone is influenced by environmental factors [23,24] and nutritional conditions [25,26] in ruminant animals. However, in the present study, the plasma concentrations of progesterone in the low P group were maintained at around 1 ng/ml, and this is similar to the level observed in abnormal conditions, such as ovarian disorders [9], stress [10], and luteal hypoplasia of Shiba goats [unpublished results].…”

Peripheral progesterone concentrations in the luteal-phase ewe: effects of a β-adrenergic receptor antagonist and two β2-adrenergic agonists

“…The progesterone radioimmunoassay method has been described by Wheeler & Blackshaw (1986) and the antiserum (11P27) by Fanti & Wang (1984). The efficiency of extraction from ovine plasma was 83-3 + 1-46% (mean ± s.e.m., « = 53).…”