EFFECT OF TEMPERATURE ON CHANGES, INDUCED BY OESTRUS, in α‐ AND β‐ADRENOCEPTOR ACTIVITIES OF THE RAT UTERUS

Abstract

The a-and 3-adrenoceptor activities of the isolated rat uterus during the oestrous cycle were intluenced greatly by temperature changes. During dioestrus, lowering the bath temperature to 250C from 400C increased two-fold the inhibition produced by (-)-adrenaline, (-)-noradrenaline, (-)-phenylephrine and (-)-isoprenaline. During oestrus adrenaline, noradrenaline and phenylephrine produced biphasic responses of contraction followed by inhibition at 40°C and isoprenaline produced only inhibition. At 250C the contractile a-responses either were abolished (phenylephrine) or greatly reduced (adrenaline and noradrenaline), while the inhibitory ,-effects of all four amines were increased.It has been generally accepted since the time of Ahlquist ( 1948) that the uterus of the rat contains f-adrenoceptors. However, Mann (1949) found that the uterus of the rat in oestrus contracted to noradrenaline and that there was a biphasic response to adrenaline. Butterworth & Randall (1970) showed that these effects are due to the presence of both at-and ,B-adrenoceptors throughout the oestrous cycle. Some workers (e.g. Rudzik & Miller, 1962;Levy & Tozzi, 1963;Tothill, 1967) have disputed the presence of excitatory ca-adrenoceptors within the normal oestrous cycle. There is now evidence that endogenous prostaglandins may be involved in motor responses of the uterus (Tothill, Rathbone & Willman, 1971;Aiken, 1972;Vane & Williams, 1973). This paper describes a study of the effect of temperature on the relative a-and B-adrenoceptor activities throughout the oestrous cycle.Methods Virgin, albino rats (Wistar strain), weighing 200-250 g, were used. The sexual state of the rat was determined by taking a vaginal smear immediately before killing by a blow to the head and bleeding out. The uterine horns were excised and 2-3 cm of the tissue from the ovarian end were set up in a 15 ml organ bath containing Tyrode solution aerated with 5% CO2 in 02. Uterine movements were recorded with an isotonic frontal writing lever (weight 0.5 g), moving on a smoked drum. Rats were used either in dioestrus or in oestrus, which was either natural or induced by oestradiol benzoate (0.5 mg s.c. given 3 days beforehand). After setting up the preparations, at least I h was allowed for the tissues to equilibrate before starting the experiment. The recordings were made at 400, 30°and 250 C. Thirty minutes were allowed to ensure that the uterus had settled down each time the bath temperature was altered. Doses were determined for each sympathomimetic amine which gave approximately 90% of a maximal contraction, or 50% inhibition of a near maximal response to acetylcholine. ResultsRats in dioestrus At the temperatures studied, all four amines produced solely inhibitory responses. At 40 C the mean inhibitory doses were phenylephrine (Phe) 12 ,g (range, 5 to 20 Mg, n = 5), noradrenaline (NA) 1.5 gg (0.75 to 2 ,g, n = 6), adrenaline (Ad) 18 ng (7 to 45 ng, n = 6) and isoprenaline (Iso) 4 ng (2 to 6 ng, n = 5). As the temperature was lowered, first to 30 C and then to 25...

Effects of estrogen and progesterone on adrenoceptors and cyclic nucleotides in rat uterus.

“…However, there is yet a controversy on the presence and significance of a-receptors in rat uterus. Some have suggested the presence of excitatory a receptors (20)(21)(22), but others have a negative opinion on this (23)(24)(25).…”