Concentrations of Oestrogen and Progesterone in the Plasma of Non-Pregnant, Pregnant and Lactating Guinea-Pigs

Abstract

SUMMARY A competitive protein-binding assay of progesterone and a radioimmunoassay of total unconjugated oestrogens were evaluated and employed in the measurement of these steroids in the plasma of guinea-pigs at different times during the reproductive cycle. Production rates (PR) were calculated from the product of the endogenous steroid concentration and its metabolic clearance rate. During the oestrous cycle, plasma progesterone levels rose from undetectable levels at the time of ovulation to 2·8 ± 0·33 (s.e.m.) ng/ml 5 days later; PR was 0·26 mg/day. During pregnancy, plasma progesterone concentrations in post-partum mated guinea-pigs rose from 15 ng/ml at day 15 post coitum (p.c.) (PR, 0·65 mg/day) to a peak value of 329 ± 14 ng/ml by days 30 to 45. The concentration fell 51–55 days p.c. (160 ± 14·7 ng/ml), but rose before parturition to 258 ± 22 ng/ml. After day 20 p.c., PR was 1·24 ± 0·3 mg/day. After parturition, plasma progesterone levels fell rapidly and during lactation were about 10 ng/ml (PR, 0·4 mg/day). Total unconjugated oestrogens in arterial plasma were not detected in early pregnancy, but rose from values of 12·8 ± 1·9 pg/ml (days 31–35) to 31·0 ± 5·2 pg/ml (days 56–60). There was a slight fall before, and a rapid one after parturition. The ratio of progesterone to oestrogen in plasma fell during pregnancy and reached its lowest values between days 55 and 60.

The effect of deslorelin acetate on the oestrous cycle of female guinea pigs

“…Opening of the membrane precedes oestrus, but its timing is too variable to be used in accurately establishing the onset of oestrus (Sisk 1976). The monophasic cyclic fluctuations of P 4 , coincident with the ovarian luteal phase (dioestrus, lack of sexual behaviour) found in the current study are in accordance with the data of others (Challis et al 1971;Garris et al 1984), whereas the E 2 levels in the current study did not show cyclic fluctuation which is in agreement with the non-cyclic fluctuation reported by Croix and Franchimont (1975). These data run counter to previous findings of Hutz et al (1990) who describe a biphasic follicular growth associated with biphasic E 2 production.…”

“…Previously, it has been shown that there is a significant elevation of plasma progesterone (P 4 ) coincident with the luteal phase (dioestrus) in guinea pigs (Feder et al 1968;Challis et al 1971;Blatchley et al 1976;Garis and Foreman 1984), whereas fluctuations of plasma oestradiol (E 2 ) levels occur throughout the oestrous cycle (Chalis et al 1971;Croix and Franchimont 1975;Garris and Foreman 1984;Westfahl and Vekasy 1988;Hutz et al 1990).…”

Progesterone Levels During the Oestrous Cycle and Pregnancy in the Cuis, Galea Musteloides

“…The progesterone levels in G. musteloides present many interesting points when compared to those of the laboratory guinea-pig as reported by Challis, Heap & Illingworth (1971). The patterns of change in plasma progesterone levels during gestation appear to be similar in the two species-relatively low concentrations are found during the first 15 days, highest levels are found at mid-pregnancy, and then somewhat lowered but yet sustained high levels are found at 51 to 60 days in the guinea-pig and 41 to 50 days in G. musteloides (Text-fig.…”

“…(2) The highest progesterone concentration found in the plasma of the guinea-pig and cuis during pregnancy is certainly very much higher than those found in many other animals such as the pregnant hamster (25 ng/ml; Leavitt & Blaha, 1970), ewe (15 to 20 ng/ml; Bassett, Oxborrow, Smith & Thorburn, 1969;Fylling, 1970) and cow (8 ng/ml; Donaldson, Bassett & Thorburn, 1970). Thus, not to mention the high level of 513 ng/ml, even the progesterone concentrations (6-3 to 15 ng/ml) during the first 15 days in guinea-pigs Challis et al, 1971) and in G. musteloides (23 to 60 ng/ml) are, in fact, high levels and the progesterone requirement during the first 15 days' gestation in both species of cavy is, therefore, by no means low compared to these animals.…”

“…Even the concentrations are similar, except during the first 14 days when the progesterone concentration in Galea is about two to three times higher than that in the guinea-pig. It has also been reported that a second increase in plasma progesterone occurred in the guinea-pig during the last few days of gestation (Challis et al, 1971). Although this is not obvious in Galea, it is not necessarily excluded, as there were too few animals for such detailed study.…”