Study of the immediate response of the adrenal cortex to corticotrophin (ACTH) is facilitated by direct sampling of the gland's venous effluent. The surgical procedures necessary to provide access to the secretion are often of sufficient severity to stimulate ACTH release from the pituitary and considerable corticosteroid secretion as a result (Holzbauer & Vogt, 1957

1. A gradually decreasing plane of light and increasing plane of darkness is not an essential factor for stimulating the onset of oestrus in sheep.2. Sheep being short-day breeding animals, a standard and regularly maintained rhythm of short-light and long-dark will stimulate the onset of oestrus.3. The terms short and long are used in the relative sense only, since their significance is solely a means of supplying the necessary contrast impulse to the pituitary gland.4. A ratio of 1 part of light to 2 parts or more of dark is sufficient to supply the contrast effect.5. Oestrous cycles induced by artificial light rhythms appear to be normal in all respects, con forming to the normal intervals between heat periods and associated with the ovulation of normal ova.6. The anoestrous period varies in depth, and sheep which have just entered it may be brought back into oestrus very much faster than animals which are in deep anoestrum.7. The milk yield of lactating ewes does not appear to be unduly depressed by the onset of oestrous periods induced by an artificial light-dark rhythm.

SUMMARY A method of transplanting a part of the pancreas into an exteriorized carotid artery—jugular vein loop in the neck of the sheep is described. Glucose and butyrate solutions were infused directly into the transplanted pancreas and shown to be powerful direct stimuli of insulin secretion by the pancreatic transplant. Patterns of insulin secretion during prolonged infusions of glucose and butyrate solutions into the pancreatic transplant are described. One of the sheep described here died 5 months after the transplantation. The other three sheep are all surviving in healthy condition 9, 12 and 18 months respectively, after the transplantation. The transplants of these three sheep continue to secrete insulin.

Previous work suggests that aldosterone is modulated by dopamine, which exerts an inhibitory effect at the level of the adrenal cortex. This study reports the effect of dopamine on aldosterone secretion in conscious sheep with cervical adrenal transplants in whom endogenous ACTH secretion was suppressed by dexamethasone. In control experiments (n = 7) local adrenal infusions of angiotensin II (AII) (1.6 ng/min for 120 min) increased aldosterone secretion to peak levels (47.8 +/- 6.8 ng/min. mean +/- SEM) at 20 min, after which secretion fell to stable levels (20-28 ng/min) at 60-120 min. On separate days, sheep were restudied (n = 5) during systemic dopamine infusions (4 microgram/kg . min for 90 min), commencing 30 min before AII stimulation. There was no significant difference, either in the pattern or the sensitivity of the aldosterone response to AII, with dopamine infusions. Large intraadrenal infusions of dopamine (10 microgram/min) also failed to alter the aldosterone response to AII. The possibility that aldosterone was already under maximum tonic inhibition by dopamine was studied in four additional experiments using the dopamine blocking drug, metoclopramide. Although the systemic (iv) administration of metoclopramide increased aldosterone in both intact and transplanted sheep, local infusions of metoclopramide (0.5-15 microgram/min intraarterially) had no consistent effect on the aldosterone response to AII, and the addition of dopamine during metoclopramide infusions also had no effect. These results indicate that local (adrenal) dopaminergic mechanisms play little or no part in the regulation of aldosterone secretion in the sheep. The mechanism whereby aldosterone secretion is increased by systemic metoclopramide remains to be explained.

Corriedale ewes in New Zealand on a constant ration throughout the year were subjected to various light treatments and their monthly growth of wool compared with controls having normal daylight hours.1. In the controls the peak of wool growth occurred during November–January with long daylight hours and the minimum during June–August with short daylight hours.