Kappa opioid-induced diuresis in female vs. male rats.

Kappa opioid agonists may produce dissimilar discriminative and analgesic effects in female vs. male subjects. The present study was conducted to determine whether a prototypic physiological effect of kappa agonists--diuresis--also differs between the sexes. When data were not corrected for individual differences in body weight, the kappa agonists U69,593 (0.03-3.0 mg/kg), U50,488 (0.3-10 mg/kg), (-)-bremazocine (0.001-0.1 mg/kg) and (-)-pentazocine (1-10 mg/kg), as well as a nonopioid diuretic, furosemide (1-10 mg/kg) produced significantly greater diuresis in normally hydrated, age-matched males than females; however, there was no sex difference in the diuretic effect of butorphanol (0.3-3.0 mg/kg), or in the antidiuretic effect of the mu agonist morphine (1.0-5.6 mg/kg, in water-loaded rats). In contrast, when data were corrected for individual difference in body weight, U69,593, U50,488, (-)-bremazocine, (-)-pentazocine, and furosemide produced nearly equivalent diuresis/kg in females and males, whereas butorphanol produced slightly greater diuresis/kg, and morphine produced significantly less antidiuresis/kg, in females than males. U69,593-induced diuresis was highly similar in males and females of similar body weight (i.e., different ages). U69,593 effects were dose-dependently antagonized by the kappa antagonist nor-binaltorphimine in both sexes, indicating a common, kappa receptor-mediated mechanism of action. (-)-Bremazocine was slightly more potent in suppressing vasopressin in 24-h water-deprived males than females. These results suggest that the greater diuretic effects of kappa receptor-selective opioid agonists in male rats are primarily due to males' larger body size (greater body water) relative to age-matched females, but may also be attributed to slightly greater vasopressin suppression in males.

Ontogeny of the sexually dimorphic area of the gerbil hypothalamus.

The sexually dimorphic area (SDA) of the gerbil hypothalamus is a set of cell groups in the medial preoptic area that is essential for masculine sexual behavior and implicated in the hormonal control of scent making and ultrasound production. The adult SDA shrinks after gonadectomy unless the gerbils receive testosterone. So does the SDA pars compacta, a small cell group in the SDA of males that is seldom seen in females. Here, development of the SDA and SDApc, and of a second, small, compact cell group, the cmSDApc, that lies caudal and medial to the SDApc, is described. Development of the SDApc and cmSDApc was studied quantitatively by assessing their incidence and volume in both sexes from birth (PND 1) to adulthood (PND 150). The volume of the entire SDA was studied from PND 45 to 150. In male gerbils, puberty begins around PND 40 and is complete by PND 90-120. The male SDA enlarged relative to the cross-sectional area of the hypothalamus as puberty began, but the female SDA did not. The SDApc was present in virtually all gerbils at birth and was the same size in both sexes. Over the next two weeks, the SDApcs of females disappeared while those of males persisted and doubled in size. Like the SDApc, the cmSDApc was larger and more common in males than in females, but it became smaller and less prevalent in both sexes during the first two weeks after birth.