An Effect of Luteinizing Hormone on the Fractional Perfusion of the Rat Ovary.

The 42K method of Sapirstein has been modified to estimate the effect of gonadotropins on ovarian fractional blood flow. Microgram doses of luteinizing hormone (LH) cause a rapid increase in the proportion of the cardiac output delivered to the ovaries; the maximum increase obtainable, about 75 %, is present about 20 min after the injection of the hormone. An effect similar to that of LH is produced by histamine, but not by FSH, of Mental Health, National Institutes of Health, prolactin, serotonin, epinephrine, or norepinephrine. The fractional perfusion of the mature rat ovary is greatest during the estrous phase of the estrous cycle. Since LH administration also enhances ovarian K uptake in the mature rat, it is possible that one function of this hormone involves the cyclic regulation of ovarian blood flow. (Endocrinology 75: 927, 1964) ~WT HEN immature rats are treated with microgram doses of a partially purified preparation of luteinizing hormone (LH), they develop ovarian hyperemia (1). This increase in the intravascular space of the ovary may be quantified by measuring the amount of 13'I-labeled albumin present in the ovary at equilibrium. It has been shown that the maximal effect obtainable, a doubling of the size of the vascular bed, is present about two hours after the administration of the gonadotropin. There is no necessary relationship between the magnitude of the intravascular space of an organ and the proportion of the cardiac output which the organ receives. The fractional blood flow of an organ (the percentage of the cardiac output which perfuses it) is determined largely by the relative arteriolar resistances of the organ and the remainder of the peripheral vascular bed. The region of the vascular bed which enlarges in hyperemia ordinarily contributes little to vascular resistance. Hence, an increase Received June 3, 1964. 1 Present address: Endocrine Unit, Massachusetts General Hospital, Boston, Mass. in the ovarian 13'I-albumin space following LH administration could represent reactive hyperemia, a consequence of decreased ovarian blood flow, as well as unchanged or increased ovarian perfusion. Techniques are now available for the estimation of organ blood flow in the intact, unanesthetized rat (2). Since changes in the proportion of the cardiac output which perfuses an organ may be of great importance in regulating how much of certain circulating substances becomes available to it (3), studies were performed on the effects of LH on ovarian fractional blood flow estimated by 42K uptake. It has been found that small doses of partially purified LH produce a very rapid increase in this index of ovarian perfusion. This increase appears to be both organand hormone-specific, and can be demonstrated in both mature and immature animals; it may thus participate in the changes in ovarian blood flow which occur during the estrous cycle. Materials and Methods Mature 160-180 g or immature 80 g Sprague-Dawley female rats were immobi-