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Biology of Reproduction, Vol 20, 648-658, Copyright © 1979 by Society for the Study of Reproduction

Relationship of Serum Estrone, Estradiol-17beta and Progesterone to LH, Sexual Behavior and Time of Ovulation in the Bitch

D. E. WILDT 1, W. B. PANKO 1, P. K. CHAKRABORTY 1, , and S. W.J. SEAGER 1

1 Institute of Comparative Medicine and Department of Cell Biology, Texas A&M University/Baylor College of Medicine, Texas Medical Center, Houston, Texas 77030


Serum estrone, estradiol-17beta and progesterone were measured in bitches in which LH, sexual behavior and laparoscopically confirmed time of ovulation had been previously studied. Steroid values from 25 estrous periods were normalized to day of peak LH (Day 0). Estrone, estradiol-17beta and progesterone concentration did not differ significantly in either dogs subjected to laparoscopy at 48 h intervals or those bitches undergoing no laparoscopy.

During the preovulatory interval, mean peripheral estrone concentrations were more variable than estradiol-17beta; however, both estrogens tended to rise gradually throughout this time period. Overall maximal estradiol-17beta concentration was detected on Day -2 with estrone peaking later (Day -0.5). Both estrogens declined (P<0.05) coincidentally with the LH surge. Progesterone from Days -14.0 through -1.5 was maintained at basal concentrations. An increase (P<0.05) in mean progesterone occurred on the day of the preovulatory LH peak which correlated with direct observation of apparent preovulatory follicle luteinization. Progesterone increased gradually from Day -0.5 through 8 and then varied for the remainder of the sampling period.

Analysis of individual cycles indicated that circulating serum concentrations of reproductive steroids fluctuated from day to day or within days of the proestrous-estrous interval. In dogs subjected to laparoscopy, initial evidence of the presence of visible preovulatory follicles was closely related to the first detectable elevations in both estrone and estradiol-17beta. Either estrone or estradiol-17beta concentrations or both surged sharply in 24 of the 25 cycles examined; however, only titers of estradiol-17beta were elevated above baseline in all cycles prior to, or at the time of, the LH peak. In 16 of 25 cycles, estradiol-17beta concentrations declined by 20 pg/ml or more 12-24 h prior to the onset of sexual receptivity. Bitches remained in estrus during periods of declining estrone and estradiol-17beta and increasing progesterone levels.

These data integrate the hormonal, ovarian and behavioral events of the estrous cycle of the bitch and suggest that: 1) a preovulatory estradiol-17beta surge exists and is likely responsible for triggering LH release; 2) estrone may play a supportive role to estradiol-17beta in the endocrine control of LH secretion; 3) preovulatory changes in follicular morphology are distinct and can be correlated with a shift from estrone and estradiol-17beta to progesterone secretion; 4) prolonged sexual receptivity in this species is supported in the presence of declining estrogen and continuously rising progesterone concentrations.

Note:
ACKNOWLEDGMENTS The authors wish to thank Dr. G. D. Niswender, Colorado State University, for supplying estradiol-17beta (#244) and progesterone (#337) antiserum and ovine LH antibody (#15), Dr. L. E. Reichert, Emory University, for providing the ovine LH (LER-1056-C2) for radioiodination and the canine pituitary LH standard (LER-1685-1) and Dr. Terry Nett, Colorado State University, for supplying technical expertise in implementing the radioimmunoassays. The computer program was the kind gift of Dr. H. E. Grotjan, University of Texas Health Sciences Center at Houston. This work could not have been completed without the valuable technical assistance of Gail Kinney, Sylvia Charman Guthrie, Pat Schmidt, Sandy Denison, Barbara Alford, Carrol Platz and Andrew Stewart. This study was supported in part by a research grant from the Ralston Purina Company, Checkerboard Square, St. Louis, Missouri.

Submitted on May 10, 1978
Accepted on October 4, 1978




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Copyright © 1979 by the Society for the Study of Reproduction.