A detailed procedure is presented for the assay of plasma progesterone. The routine assay is based on the use of antiserum which is covalently linked to microcrystalline cellulose, the double-antibody method being used as a reference separation system. This procedure gives high precision accompanied by small and acceptable losses of antiserum titre but without loss of sensitivity when compared with the double-antibody method. Ethanol is first added to the plasma (10vol. of plasma+1vol. of ethanol) after which a single extraction with light petroleum yields a constant recovery [92.4+/-1.2 (s.d.)% of added [(3)H]progesterone] and obviates the need for tracer recoveries on each sample being assayed. Distortions of the response curve owing to solvent residues have been almost eliminated. The assay can measure progesterone at all stages of the menstrual cycle when volumes of 200mul of plasma are used and this permits the detection of the periovulatory rise at its inception. Detailed specificity studies are presented for the assay end point itself and these are related to the responses to be expected in extracts of plasma. Progesterone-like activity was found in urine and a fourfold increase in excretion rates was observed between the follicular and luteal phase of the normal menstrual cycle.

A method for the production of highly substituted prostaglandin-bovine serum albumin conjugates has been developed.2 Antisera to prostaglandins B2 and F2o, were raised in rabbits immunized with prostaglandin-bovine serum albumin conjugates. 3 The antisera were assessed for specificity and sensitivity by the double antibody radioimmunoassay method and after they were covalently linked to powdered cellulose to form a 'solid-phase' system. 4 Solid phase radioimmunoassays were developed using conventional shaking and in the presence of sucrose which obviates the need for continuous mixing of the incubates.

1. Hypertension produced in two-kidney Goldblatt dogs was accompanied by a transient fluid retention, reaching a maximum 4 days after clamping. 2. Prostaglandin E and F concentrations in venous blood from the intact kidney also rose transiently, showing a maximum by the fifth day. 3. The rise in prostaglandin release from the intact kidney may be related to the fluid retention.

Renal autoregulation of blood flow was re‐examined in the pump‐perfused canine kidney and concentrations of prostaglandins E and F in the renal venous plasma were measured by radioimmunoassay. At low perfusion pressures, below the range of autoregulation, prostaglandin E and F concentrations rose and calculated prostaglandin E secretion rate fell. Meclofenamate (10 mg/kg, i.v.) reduced renal blood flow and prostaglandin E and F secretion rates, but did not abolish autoregulation. Renal prostaglandins do not appear to mediate autoregulation in the kidney but may affect the level at which flow is controlled.