PERIPHERAL PLASMA OESTRADIOL AND LUTEINIZING HORMONE CONCENTRATIONS DURING THE OESTROUS CYCLE OF THE RAT

Abstract

Plasma was obtained from adult Wistar rats maintained under 14 h of light and 10 h of darkness and shown by daily vaginal smears to have had two or more cycles of 4 days ' duration. Oestradiol-17\\g=b\\concentrations were measured by a micro\\x=req-\\ modification (Exley, 1969) of the competitive protein binding technique of Corker & Exley (1970). In more than 75 % of cases plasma from two rats was pooled (5-7 ml) and duplicate determinations carried out. At concentrations above 10 pg/ml the average variation between duplicates was \\m=+-\\15%of the mean. Below this level, although the mean detectable amount was 6 pg (corresponding to a concentration of about 2 pg/ml) precision was such (average agreement between duplicates\\m=+-\\35%) that values in this range must be regarded as estimates only. Plasma luteinizing hormone (LH) in samples from individual rats was determined by a modification(Naftolin & Corker, 1970) of the radioimmunoassay method of Niswender, Midgley, Monroe & Reichert (1968). Duplicates agreed to within 10 % and all samples measured were well within the sensitivity of the method. Beginning at about- 15.00 h on the day of dioestrus there was a sustained rise in plasma oestradiol concentration (Fig. 1). Highest values were found in samples