Development and fate of transferred rabbit ova or blastocyst in relation to the ovulation time of recipients

Publisher Summary This chapter focuses on the interactions between estrogens and progesterone. The two female sex hormones—the estrogenic and the progestative substances—do not act independently. They are bound by functional relations, which constitute one of the many aspects of the vast problem of endocrine balance. It has been shown that the joint action of the two female hormones can determine mating. The females of different species do not behave in a uniform manner. In all species, estrogen produces heat to a greater or lesser extent, but in some, namely the goat and sheep, progesterone opposes this action. In others, on the contrary, progesterone reinforces the action of estrogen; this synergistic action is found in the guinea pig, in the rat, in the mouse, and in the golden hamster. In this chapter precise examples have been given of hormonal synergism between estrogen and progesterone. Hypotheses have been formulated to explain the mechanism of this synergism. It has also been suggested that estradiol can assist the action of progesterone because it increases the circulation of blood in the uterus.

Interactions between estrogens and progesterone.

Many substances have been shown to affect the smooth muscle cell contractions in the uterus eg catecholamines oxytocin prostaglandins angiotension 2 and acetylcholine have been implicated The sole action of adenosine cyclic 35 monophosphate (cAMP) is thought to be the activation of cAMP-dependent protein kinase(s) These enzymes catalyze the transfer of the gamma-phosphate of ATP to a serine or threonine residue of specific protein substances cAMP-dependent protein kinases are widespread and are present in both the endometrium and myometrium They are composed of regulatory and catalytic subunits cAMP binds to the regulated subunit dissociating the complex to yield the active catalytic subunit Isoproterenol in isolated myometrium increased cAMP levels decreased unsaturated cAMP binding sites and increased cAMP-dependent protein kinase activity but decreased total protein kinase activity as measured in thepresence of cAMP The protein kinase activity could be resotred by treatment with noionic detergent Triton X-100 Maximal detergent-dependent protein kinase activity has been found to be associated with the 20000-50000 XG ultracentrifugal sediment This fraction consisted of a mixture of membranes and was enriched in ATP-dependent C++ transport activity Both cytosol and membrane protein kinase activity were Mg++-dependent but the membrane form required a 5-fold concentration The membrane form was almost totally dependent on the nonionic detergent Triton X-100 for activity At concentrations greater than 1% Triton X-100 progressively inhibited membrane protein kinase activity A similar pattern of detergent inhibition was shown for the cytosol enzyme In the absence of Triton X-100 the membrane fraction completely suppressed enzyme activity present in the cytosol Expected activity was recovered in the presence of Triton X-100 Subsequent experiments showed that the process was temperature-dependent The migration of protein kinase from the cytosol to nuclear sites as a result of cAMP activation has been described in other tissues ovary adrenal and liver This translocation may be the mechanism by which the protein kinase localizes its physiological substrates Other studies suggest a central role in Ca++ transport a mechanism for the control of muscle contraction at the membrane level Results of other studies show tractile apparatus and the ATP-ase activity in smooth muscle cells A sequence of events as envisioned in the hormonal regulation of myometrial contractility at the molecular level is presented Study of the process of parturition suggests that agonists have redundant self-enhancing stimulatory mechansims to ensure that coordinated powerful uterine contractions are generated causing the fetus to be delivered

The Role of Cyclic AMP in the Regulation of Smooth Muscle Cell Contraction in the Uterus

The Effect of Posterior Lobe Pituitary Gland Fractions on the Intact Human Uterus

Abnormal uterine action in labour.

http://ajplegacy.physiology.org/content/ajplegacy/92/2/420.full.pdf

Samuel R. M. Reynolds

Papers

STUDIES ON THE UTERUS: I. A Method for Recording Uterine Activity in Chronic Experiments on Unanesthetized Animals

Studies on the uterus : V. The influence of the ovary on the motility of the non-gravid uterus of the unanesthetized rabbit

STUDIES ON THE UTERUS: III. The Activity of the Uterine Fistula in Unanesthetized Rabbits Following Coitus and During Pseudopregnancy

STUDIES ON THE UTERUS: II. Responses of the Non-Gravid Uterus of the Unanesthetized Rabbit to Pituitrin and Pitocin

STUDIES ON THE UTERUS: VI. The Effect of Oestrin on the Uterine Fistula During Pseudopregnancy