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Biology of Reproduction, Vol 24, 839-845, Copyright © 1981 by Society for the Study of Reproduction

Relationship Between Progesterone and Prolactin Surges in Aged and Young Pseudopregnant Rats

DENNIS P. GILMAN 1, JOHN K. H. LU 1, DAVID I. WHITMOYER 1, HOWARD L. JUDD 1, , and C. H. SAWYER 1

1 Department of Anatomy, Department of Obstetrics and Gynecology, and the Laboratory of Neuroendocrinology, Brain Research Institute, UCLA School of Medicine, Los Angeles, California 90024


The 24 h patterns of prolactin (PRL), progesterone (P), and 20agr-hydroxyprogesterone (20agr-OH-P) secretion were determined on Day 7 of pseudopregnancy in old (20-26 months) and young (4 months) rats and 2 days after ovariectomy (OVX; Day 8) on Day 10, with or without P replacement. Serial blood samples were taken via intra-atrial cannula for measurement of plasma hormone levels. In old, repetitively pseudopregnant (RPSP) rats, PRL increased from baseline values to 446 ± 84 (SEM) ng/ml at 0200 h and subsequently fell to 49 ± 10 ng/ml by 0800 h. Following OVX and implantation of blank Silastic capsules, plasma PRL remained low throughout Day 10; however, the nocturnal PRL surge was maintained in animals implanted with P capsules. In contrast, young rats made pseudopregnant by cervical stimulation (CS-PSP) or estradiol benzoate administration (EB-PSP) exhibited both diurnal and nocturnal PRL surges at 1700 and 0200 h, respectively, with peak nocturnal PRL values almost twice as high as those in old RPSP females. OVX abolished both PRL surges in EB-PSP females, but not the nocturnal surge in CS-PSP animals.

Plasma concentrations of P ranged from 48 to 82 ng/ml in all three pseudopregnant (PSP) groups, while 20agr-OH-P levels ranged from 41 to 64 ng/ml in the young PSP animals. Old RPSP females showed a rise in 20agr-OH-P (98 ± 15 ng/ml) at 2000-2300 h. P capsules in OVX-PSP rats maintained plasma P and 20agr-OH-P at half the concentrations seen in intact animals.

These results reveal that 1) old RPSP rats show nocturnal PRL surges, but not both diurnal and nocturnal surges as seen in young PSP females; 2) the PRL surge in old rats is closely dependent on intact ovarian function, as are both surges in EB-PSP females and the diurnal surge in CS-PSP animals; 3) levels of circulating P about half those found in the PSP state are sufficient to maintain the nocturnal PRL surge in OVX, old RPSP rats and both surges in OVX EB-PSP animals.

Note:
ACKNOWLEDGMENTS The authors wish to thank Ms. Peggy Chappus for technical assistance, Mr. Bob McAlister for the illustrations, and Ms. Lois Fels for assistance in the preparation of the manuscript. We are especially grateful to Ms. Marianne Lu and Mr. Walker Birrell for expert assistance in the progestin RIAs. The reagents used in the PRL RIA were generously supplied by the NIAMDD Rat Pituitary Hormone Distribution Program and Dr. A. F. Parlow.

Submitted on November 14, 1980
Accepted on January 15, 1981






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Copyright © 1981 by the Society for the Study of Reproduction.