Ovarian Blood Flow in the Rat: Association with Body Weight, the Estrous Cycle, and Pseudopregnancy

The relationships of ovarian blood flow (OBF) to ovarian function, body weight, cyclic state, and age of the corpus luteum were studied in aging rats with acutely implanted electromagnetic blood flow probes. Ovarian function was monitored by estimation of serum 17-β-estradiol (E₂) and progesterone (P) levels during (i) different stages of body maturation as indexed by body weight, and (ii) various stages of the estrous and pseudopregnancy (PSP) cycles. A distinct elevation in basal OBF rates was observed to occur in relation to body weight/age. Basal OBF rates and body weight exhibited a near linear correlation (r = 0.985; P ≤ 0.001) between 200 and 260 g, with a rise in mean basal OBF rates from 1.1 to 3.2 ml/min occurring in Day-8 PSP rats (Day 0 = ovulation). In weight-regulated (≥ 250 g) cycle rats, OBF increased in parallel with serum E₂ levels during the proestrus-estrus period in association with ovulation, and subsequently declined to basal levels on diestrus. In PSP rats, OBF remained elevated between Days 1 and 8, during the period of peak luteal function. Between Days 8 and 12, both OBF and luteal function declined in a parallel manner as the ovary prepared for the subsequent ovulatory period. These results indicate that during the estrous cycle, OBF rates and serum E₂ levels rise in a parallel manner, whereas during PSP, serum P levels and OBF are positively correlated. The parallel decline in OBF and serum P during luteolysis suggest that both parameters are functionally related and may be regulated by either a systemic or intraovarian controlling mechanism.