Gender differences in the blood volume of conscious Sprague-Dawley rats.

Reference values of blood volume (BV) and plasma volume (PV) of animal species are given as functions of body weight and gender specification generally is not given. Considering the common observation of a decreased hematocrit (Hct) in the females of many species, the BV, the PV, or both must differ between genders. The present study was performed to determine the magnitude of those differences. We measured Hct and PV in 24 female and 23 male Sprague-Dawley rats in their 12th week of life. The rats were surgically prepared with indwelling femoral arterial catheters 4 d prior to the determination of BV. Evan's Blue dye dilution was used to determine PV in conscious, quietly resting animals. BV was calculated as PV/(1-Hct). Mean Hct was 2% lower in female rats than males, and PV (mean +/- 1 standard deviation) was 4.86 +/- 0.54 ml/100 g in females compared with 4.12 +/- 0.32 ml/100 g in males. Calculated BV in female rats was 7.84 +/- 0.70 ml/100 g compared with 6.86 +/- 0.53 ml/100 g in males. When precise estimates of BV or PV are needed for research or dosing purposes, gender differences of 18% for PV and 14% for BV must be considered. In addition, species other than the rat may have similar discrepancies between sexes, and the prudent investigator must determine individual volume assessments of both sexes before assumptions of BV and PV for a species can be made.

Effects of prenatal ethanol exposure and sex on the arginine vasopressin response to hemorrhage in the rat.

AVP synthesis, storage, and osmotically stimulated release are reduced in young adult rats exposed prenatally to ethanol (PE). Whether the reduced release of AVP to the osmotic stimulus is due to impairment of the vasopressin system or specifically to an osmoreceptor-mediated release is not known. The present experiments were done, therefore, to determine whether a hemorrhage-induced AVP response would also be diminished in PE-exposed rats. Pregnant rats were fed either a control liquid diet [no prenatal ethanol (NPE)] or a liquid diet with 35% of the calories from ethanol from days 7-21 of pregnancy. Offspring were weaned at 3 wk of life. At 11 wk of age, femoral arterial catheters were surgically placed, and blood volumes were determined at 12 wk. Three days later, two hemorrhages of 10% of the blood volume were performed with samples taken before and 10 min after the hemorrhages. After a 20% blood loss, plasma AVP was 19% higher in NPE rats than in the PE rats despite no differences in mean arterial blood pressure (MABP). Also, hypothalamic AVP mRNA and pituitary AVP content were reduced in PE rats. Furthermore, confirming an earlier report of sex differences in AVP release, the hemorrhage-induced hormone response was twofold greater in female rats than male rats, regardless of previous ethanol exposure. These studies demonstrate that the AVP response to hemorrhage is reduced in PE rats independently of differences in MABP. The data are compatible with a theory of a reduced number of hemorrhage-responsive vasopressinergic neurons capable of stimulated AVP release in PE rats.