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A study of the metabolism of oestradiol in the human endometrium and myometrium of the proliferative and secretory phases of the cycle showed that the conversion of oestradiol to oestrone by endometrium in the proliferative phase was higher than that in the secretory phase. The decreased metabolic activity of the secretory phase endometrium was attributed to the influence of progesterone on the endometrium. The metabolic conversion of oestradiol to oestrone was enhanced when pyridine nucleotides were added to the system. The conversion of oestradiol to oestrone was maximum in the cytoplasmic and nuclear fractions of the endometrium. Furthermore, the conversion of oestradiol was low in all the subcellular fractions of the myometrium as compared with the endometrial subcellular fractions. The presence of co-factors increased the metabolic conversion of oestradiol to oestrone in the subcellular fractions of the endometrium. The presence of 17 beta-hydroxysteroid oxidoreductase was indicated in all the subcellular fractions. A correlation was found between the amount of oestradiol and oestrone bound to the receptors in the uterus and the rate of metabolism of oestradiol in the uterus. The physiological significance of metabolism of oestradiol and the hormone action are discussed.

Catecholamine stimulation of adenyl cyclase in plasma membranes from rat myometrium was typical of beta-adrenoceptor stimulation. Thus, isoproterenol was the most potent followed by epinephrine and norepinephrine; phenylephrine, a pure alpha-agonist, did not activate the enzyme. The catecholamine-induced activation was potently inhibited by propranolol, whereas phenozybenzamine was without effect. The ED50 for 1-isoproterenol activation was 10- minus 7 M. Binding of [3H]-d-isoproterenol to the same preparations bore little resemblance to the pattern of 1-isoproterenol activation of adenyl cyclase. Propranolol, even at high concentrations, was without significant effect. The degree of binding was inversely rflated to the osmolarity suggesting that diffusion may have contributed to the binding. This contention was further supported by the time course of binding which was biphasic- the first component (smaller than 4 min) being less affected by osmolarity than the second (greater than 4 min). The optimum pH for binding was 7.4.