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Summary. Tissue levels of cyclic AMP were measured in rat corpora lutea at various times after administration of LH in vitro and in vivo. In-vitro addition of LH produced more pronounced accumulation of cyclic AMP in very young corpora lutea (1-day-old) than in the older corpora lutea (3- and 7-day-old). When LH was administered in vivo the highest accumulation of cyclic AMP was seen in the older corpora lutea (7- and 3-day-old).
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Search for other papers by G. SELSTAM in
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Summary.
A technique for perfusion of the rabbit ovary in vivo is described which allows a quantitative determination of the intra-ovarian passage from artery to vein of 15 ± 5 μm non-radioactive microspheres. The passage of microspheres was less than 1 % in ovaries containing follicles (from non-pregnant rabbits) as well as in ovaries containing CL (from rabbits in different stages of pseudopregnancy). Addition of a vasodilator to the perfusion system did not influence the result.
The present results do not indicate that arterio-venous shunts of physiological significance exist in the rabbit ovary.
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To assess the effects of prostaglandins and prolactin on corpus luteum function and regression, sterile-mated adult pseudopregnant rats hysterectomized on day 5 after mating were injected with indomethacin or prolactin. Daily samples of blood were collected via the tail, from day 12 to day 21, and assayed for serum concentrations of progesterone, 20α-dihydroprogesterone and LH, whereafter corpora lutea and the remainder of ovaries were separated and the tissue content of PGF2α, PGE2 and LH receptor mRNA were measured. Injections of prolactin (8 iu) s.c. or a low dose of indomethacin (200 μg kg−1) s.c. were administered twice a day, beginning on day 13 after mating. Both indomethacin and prolactin significantly increased serum progesterone concentrations (P < 0.05; n = 8), and extended the period of functional corpora lutea when compared with controls. Indomethacin, but not prolactin, lowered the concentration of serum 20α-dihydroprogesterone. In the corpora lutea of indomethacin-treated animals, collected on day 21, both prostaglandins measured were reduced in concentration by 50% or more, compared with controls (P < 0.05; n = 8), whereas prolactin had no effect. Both prolactin and indomethacin treatment caused a substantial (tenfold) increase in the concentration of LH receptor mRNA, confined solely to the luteal compartment. These findings in vivo provide further evidence for a luteolytic role of locally synthesized prostaglandins in the rat ovary. Furthermore, prolactin can sustain corpus luteum function by exerting a luteotrophic effect during the late luteal phase, as judged by the stimulation of progesterone synthesis and the expression of LH receptors.
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Summary.
After perfusion of 10 rabbit ovaries in vitro with a modified Krebs bicarbonate buffer containing dextran and glucose, the concentration of cAMP in the perfusion medium was significantly increased 2·5 min after stimulation with 10 μg LH/ml medium and was higher at 15 and 30 min. Intravenous injection of 100 μg LH/rabbit caused a significant increase of cAMP concentrations in the ovarian venous blood from 8 ovaries 10 min after the injection and the cAMP concentrations were higher after 15 and 30 min. The ovarian blood flow was not changed after the LH injection. It is concluded that perfusion techniques can be useful in analysis of the mechanisms and physiological significance of release of cAMP from the ovary after hormonal stimulation.
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Search for other papers by M. Gåfvels in
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Summary. Noradrenaline infusion for 2 min (0·4 μg/min) in anaesthetized rats increased the vascular resistance in 6-day-old corpora lutea, but had no significant effect on the vascular resistance in young (2-day-old) or old corpora lutea (11 days old). The luteal blood flow of the control rats was higher in 6-day-old corpora lutea than in those of 2 and 11 days. The luteal blood flow apparently lacks autoregulation, since a linear relationship between blood flow and arterial blood pressure was registered. The present study shows that, besides the well known metabolic effects of catecholamines on corpus luteum function, catecholamines can exert acute vascular effects, but only on the corpus luteum of pseudopregnancy in the middle of its life span.
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Search for other papers by G. Selstam in
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Summary. Luteal β-adrenergic receptor concentration and subtype were determined in adult pseudopregnant rats during and after the period of the functional luteal phase. The specific β-adrenergic receptor ligand (−)-3-[125I] iodocyanopindolol ([125I]ICYP) was used to determine the receptor concentration in corpora lutea of adult pseudopregnant rats. A 3-fold increase in β-adrenergic receptor concentration was seen during the first 2–3 days of pseudopregnancy, whereafter the receptor concentration declined. During the functional luteal regression period (Day 12–15) the receptor levels were still low. In regressed (Day 16–22) corpora lutea a temporary increase in β-receptor concentration was seen which may represent some role for β-adrenergic mechanisms in the regulation of morphological regression in the corpus luteum.
To determine the β-adrenergic subtype, competition of [125I]ICYP-binding with selective β1- and β2-adrenergic antagonists was assessed in corpora lutea of different ages and in rat heart and uterus. The β-adrenergic receptors in corpora lutea of adult pseudopregnant rats were shown to be solely of the subtype β2, regardless of the luteal age.
Keywords: β-adrenergic receptor; subtype; corpora lutea; rat; luteal phase
