LH-SECRETORY RESPONSES CAUSED BY CONTINUOUS INFUSION OF LH-RH IN PSEUDOPREGNANT RATS

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Abstract
The LH[luteinizing hormone]-secretory response (LH-SR), caused by (standard) infusion of LH-RH [LH-releasing hormone], was estimated throughout pseudopregnancy (PSP) as well as on diestrus-1 and -2 of the 4 day estrous cycle. The LH-SR was judged according to 3 parameters: mean maximal plasma LH concentration (height, expressed in ng LH-RP-1/ml plasma); mean area under the curve (AUC, expressed in area units); and a composite, dimensionless parameter: RQ (response quotient), defined as height/AUC. This latter parameter informs on the shape of the curve. The LH-SR on day 1 of PSP and diestrus-1 were both relatively low (.apprx. 350 ng LH-RP-1/ml plasma) and characterized by the same RQ (about 12). On days 2, 5, 7 and 9 of PSP the LH-SR were essentially the same and appeared to have characteristics of the LH-SR of both PSP-1 and diestrus-1 (RQ) and diestrus-2 (height, .apprx. 1000 ng LH-RP-1/ml plasma). From day 10, on the LH-SR became increasingly higher (PSP 11, .apprx. 1900 ng LH-RP-1/ml plasma; PSP 12, .apprx. 3300 ng LH-RP-1/ml plasma) and steeper (RQ, .apprx. 22). At the end of PSP the spontaneous LH-surges were measured. These appeared to be very high if compared to those which are generated in 4 day cyclic rats (.apprx. 5800 ng LH-RP-1/ml plasma). A period of PSP is not simply an ovulatory cycle of which the diestrous phase is extended by about a week. Active corpora lutea apparently secrete, next to progesterone, substances which play a key role in the regulation of the secretion of LH in the course of PSP.