This work was done during the tenure of an Agricultural Research Council Scholarship (F.W.H.) and an I.C.I. Fellowship (J. S. L.). Financial assistance from the Nuffield Foundation is gratefully acknowledged.

Summary. Anoestrous and cyclic ewes were treated with luteinizing hormone-releasing hormone (LH-RH) by intravenous (i.v.)

It is now shown that such serum has a similar effect in dogs, a pig and a lamb and that in the pig and the lamb this hyperglyeaemia coincides with the disappearance of biologically active insulin from the blood. METHODSSera. Guinea-pig anti-insulin serum was obtained from animals treated with recrystallized bovine insulin (Robinson & Wright, 1961) and assayed for insulin-neutralizing potency in conscious fed rats (Armin et al. 1960a 25 mg = 0-5 ml./kg).Pig: a Large White pig (male; 26 kg) with pentobarbitone sodium (Veterinary Nembutal, Abbott Laboratories; 30 mg = 0*5 ml./kg) anaesthesia being maintained by smaller doses injected intravenously as required. Local procaine (2 g/100 ml.) anaesthesia was used to introduce polythene catheters (internal diameter, 0-023 mm., size PE 10, Clay Adam Co. Inc.) into a vein and an artery; the femoral vessels were used in the dogs and smaller superficial vessels in the hind limb of the pig.Lamb: a Hampshire lamb (female, 24 kg) had a similar catheter inserted through a needle into the external jugular vein; this animal received no general anaesthetic and was restrained in a specially constructed stock. The catheters were connected by way of Perspex three-way taps (Armin & Grant, 1953) to an infusion pump (Armin et al. 1960b) and were kept patent by slow infusions of NaCl solution (0 9 g/100 ml.). Fluids were injected and blood samples drawn through these taps, which also permitted measurement of mean arterial pressure with the mercury manometer.Sugar estimations were carried out on blood samples (0-2 ml.) by a modification (Wright, 1957) (Somogyi, 1945). Both methods were used to determine the sugar content of some of the blood samples and similar results were obtained.Plasma-insudin activity. The experimental procedure used to determine the glucose consumption rates of rat hemi-diaphragms was similar to those described by Vallance-Owen & Hurlock (1954) and Wright (1957); a more detailed account will be published elsewhere. Albino rats of a Wistar strain (125-200 g) were deprived of food but not of water for 24 hr and decapitated. The hemi-diaphragms were quickly removed and soaked for 10 min at room temperature (20-250 C) in a bicarbonate-buffered medium (Gey & Gey, 1936) containing glucose 0-25 g/100 ml. Each hemi-diaphragm was blotted and placed in the incubation medium (1 ml.) in a flask (gassed with a mixture of 95 % 03 and 5 % CC2) and then

1. Some of the effects of stress, fasting and ACTH injections in pregnant ewes were investigated.2. A 6-day fast produced a relatively mild hypoglycaemia and hyperketonaemia without inducing pregnancy toxaemia.3. Stress of transport produced an immediate slight rise in plasma cortisol; 4 hr. later the plasma cortisol had returned to the pre-stress levels.4. A combination of stress and fasting produced severe hypoglycaemia, hyperketonaemia and subacute pregnancy toxaemia, but there was no increase in plasma cortisol levels.5. Daily injections of ACTH resulted in a fourfold increase in plasma cortisol and prevented the development of hypoglycaemia, severe hyperketonaemia, and pregnancy toxaemia in pregnant ewes subjected to stress and fasting.6. Changes in plasma concentrations of NEFA, urea, proteins, catecholamines and insulin were also investigated.

Although the changes occurring in the plasma levels of progesterone and LH during the oestrous cycle of sheep have been well documented, there is some doubt about the pattern of plasma FSH concentrations. We present some data on the levels of all three hormones in a limited number of plasma samples taken from ewes experiencing normal oestrous cycles. Eight 3-year-old Cheviot ewes were kept in a paddock with a vasectomized ram during October and November. The ram was fitted with a marking harness and the coloured crayon on the harness was changed every 15 days. The ewes were examined daily and the day that a ewe was first marked by the ram was designated Day 0 of the cycle. Blood samples were taken from the jugular vein into heparinized 10 ml Vacutainers (Becton-Dickinson U.K. Ltd) and were centrifuged at 4\s=deg\Cwithin 1 hr. Plasma was stored at