Hormonal influence on the response of the uterus of the Brazilian marsupial Didelphis albiventris to adrenergic drugs.

The influence of catecholamines on the estrogenized uterus of the Didelphis albiventris was studied in an in vitro preparation. It was observed that the D. albiventris uterus reacts to both alpha and beta-adrenergic agonists but not dopaminergic ones. Adrenaline is more potent in inducing a contractile response than is noradrenaline. Isoprenaline, when added to the bath, is able neither to induce a response nor to interfere with a contraction previously induced by acetylcholine. It is, however, able to block the contractile response brought about by electric field stimulation. In an in vitro preparation from animals previously treated with estrogen and progesterone, the sensitivity to both alpha- and beta-adrenergic drugs was greatly increased. This is demonstrated by a higher pD2 in progesteronized animals compared to that in estrogenized ones. The increased sensitivity to beta-agonists after progesterone treatment is illustrated by the fact that isoprenaline is effective in inducing a relaxation of the uterus, in these conditions. These results indicate that the Brazilian opossum should be included among those animals in which progesterone enhances uterine sensitivity to drugs.

Influence of estrogen and progesterone on the uterine sensitivity in vitro to neuropituitary hormones in the Brazilian marsupial Didelphis albiventris: comparison with lactating animals.

The influence of different neuropituitary hormones on the contraction of the Brazilian opossum uterus in vitro was studied in spayed adults injected with (i) peanut oil (ii) estrogen or (iii) estrogen plus progesterone, and in a fourth group of lactating animals. Two parameters were analyzed from the dose-response curve: pD2 and the relative contractile response compared to the maximal one induced by oxytocin. When oxytocin was administered to the bath, neither pD2 nor the contractile force was affected by any hormonal treatment or lactation. Oxytocin, however, remained in any hormonal status, the most powerful agonist to induce uterine contraction. Lysine vasopressin was the weaker agonist in any hormonal status. It binds slightly less to the isolated uterus than to the hormone-treated one. The maximal contractile force remains unchanged when the uterus is from ovariectomized or steroid-treated animals. However, after lysine vasopressin, uterus from lactating opossum develops a less intense contractility than that observed in other groups. Arginine vasopressin induces a contractile force comparable to that induced by oxytocin in any hormonal status. The affinity of this peptide for the uterine receptor is significantly lower in ovariectomized and estrogen-treated animals; after progesterone injection or in lactating animals the receptor affinity for this hormone is increased to the level of the affinity for oxytocin. Receptor affinity for arginine vasotocin is reduced in any hormonal state and brought to a level comparable to that for oxytocin only in lactating animals. On the other hand, progesterone reduced the maximal contractile force induced by this neuropeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological and physiological factors involved in the contractility of the spermatic cord and ductus deferens of the opossum (Didelphis albiventris).

The opossum spermatic cord is characterized by a thick skeletal muscle coat, provided by the great development of the cremasteric muscle. Acetylcholine induced a powerful contraction of the spermatic cord placed in an organ bath containing Heller's solution. This contraction was blocked by curare but not completely by atropine as is usual for skeletal muscle. However, the ductus deferens did not respond to acetylcholine or catecholamines under the same conditions. Specific histochemical methods for both catecholamines and acetylcholinesterases revealed that the ductus deferens musculature, composed mainly of circular fibres, is richly innervated by adrenergic and presumed cholinergic nerve fibres. The lack of responsiveness to the neurotransmitters could be explained by the absence of longitudinally arranged muscle. It is suggested that in the opossum the cremaster could participate in the mechanism of sperm transport.