Endocrinology, Vol 96, 1241-1246, Copyright © 1975 by Endocrine Society

ARTICLES

Serum prolactin and LH in early phases of delayed versus direct pseudopregnancy in the rat

JE Beach, L Tyrey and JW Everett

Delayed or direct pseudopregnancies were induced by electrical stimulation of the cervix at 1400 h on diestrus day 2 (D-2) or on estrus, respectively. Blood samples for measurement of prolactin and LH by radioimmunoassay were collected by rapid decapitation at 5, 15, 30, 45 or 60 min after cervical stimulation or thereafter at 3-h intervals throughout the first 6 days of leukocytic vaginal smears of pseudopregnancy (PSP L-1 to L-6). For comparison, untreated animals were decapitated at the same 3-h intervals throughout the 4-day cycle. Serum LH concentrations in all the experimental animals did not vary from those measured in the cyclic controls. Compared with the normal cycle, prolactin (PRL) levels were not different until 10 h after cervical stimulation during estrus. After stimulation on D-2, PRL secretion did not differ from that in the normal cycle until approximately 37 h later, when there was a short rise following the usual proestrus surge. In both direct and delayed pseudopregnancy, twice-daily PRL surges appeared on L-1 and, except for a missing nocturnal surge on L-2 in delayed PSP, continued regularly through L-6. The absence of any immediate increase of PRL following the D-2 stimulus strongly supports the view that information from the stimulus is retained in the central nervous system to be expressed later after a set of new, competent corpora lutea has been formed.