SUMMARY1. Vasopressin and oxytocin have been measured in the neurohypophysis of rats which had either been given a 2 % (w/v) NaCi solution to drink or been deprived of drinking water for up to 5 days.2. There was a progressive decrease in the vasopressin content of the glands in both groups; the rates ofdepletion were not significantly different.3. Oxytocin also decreased progressively in both groups but the glands from the 'saline-treated' rats contained less hormone than those from the 'water-deprived' animals.4. The differences in gland content of oxytocin could not be correlated with differences between the plasma osmolalities or sodium concentrations of the two groups.

Acid extracts of corpora lutea collected from nonpregnant cows were found to contain oxytocin, arginine vasopressin, and neurophysin. The inhibition curves of the oxytocin and vasopressin extracts showed parallelism with the appropriate standard preparations in specific RIAs and eluted at the same position as the standards using high performance liquid chromatography (HPLC). The neurophysin extract showed parallelism in a bovine neurophysin I RIA and had a similar elution position to the standard on both Sephadex G-50 and HPLC. However, its immunoreactive profile on HPLC differed slightly from that obtained with hypophyseal bovine neurophysin I. In nonpregnant cows the oxytocin content (about 1 microgram g-1 wet wt of tissue) was three orders of magnitude greater than the vasopressin content. Levels of luteal oxytocin were considerably lower in pregnant animals. These results show that the bovine ovary is a rich source of neurohypophysial peptides and suggest that oxytocin biosynthesis may occur within the corpus luteum.

1. Rat neurohypophysial extracts have been examined by polyacrylamide-gel electrophoresis. 2. Three of the proteins were tentatively identified as neurophysins by their acidic nature and their disappearance after dehydration of the animals. 3. These proteins were radioactive 24h after intracisternal injection of [(35)S]cysteine. 4. Two of the proteins were present in much greater quantities than the third, and these two were present in the gland in the same ratio as the hormones vasopressin and oxytocin. 5. One of these proteins was absent from glands of rats homozygous for diabetes insipidus but present in heterozygous animals. 6. It is suggested that these two proteins are the vasopressin-neurophysin and oxytocin-neurophysin of the rat.

Bovine ovaries were obtained from the abattoir and corpora lutea were classified as: (1) early luteal phase (approximately Days 1-4); (2) mid-luteal phase (Days 5-10); (3) late luteal phase (Days 11-17); (4) regressing (Days 18-20) and (5) pregnant (Days 90-230). In addition, preovulatory follicles and whole ovaries without luteal tissue were collected. Concentrations of oxytocin, vasopressin, bovine neurophysin I and progesterone were measured in each corpus luteum by radioimmunoassay. Progesterone and neurophysin I levels increased from Stage 1 to Stage 2, plateaued during Stage 3 and declined by Stage 4. Oxytocin and vasopressin concentrations increased from Stage 1 to Stage 2 but declined during Stage 3 and were low (oxytocin) or undetectable (vasopressin) in follicles, whole ovaries and pregnancy corpora lutea. Therefore the concentrations of both peptide hormones were maximal during the first half of the cycle and declined before those of progesterone. The high concentration of oxytocin within the corpus luteum coupled with the presence of bovine neurophysin I suggests that oxytocin is synthesized locally.

The long-term effects of oxytocin administration on the testis were studied using intratesticular implants. Adult male rats had an Accurel device containing 20 micrograms oxytocin (releasing approximately 200 ng/day) implanted into the parenchyma of each testis; control animals received empty devices. The animals were killed at weekly intervals for 4 weeks. Some animals were perfused and the testes processed for light and electron microscopy. Blood was collected from the remaining animals for the measurement of testosterone, dihydrotestosterone, LH, FSH and oxytocin; epididymal sperm counts were measured and the testes were extracted and radioimmunoassayed for testosterone, dihydrotestosterone and oxytocin. Long-term administration of oxytocin resulted in a significant reduction in testicular and plasma testosterone levels throughout the 4-week period examined and, after 14 days of treatment, lipid droplets were seen in the Leydig cells of treated but not control animals. Concentrations of dihydrotestosterone in the plasma and testes of the oxytocin-treated animals, however, were significantly elevated after 7 and 14 days and at no time fell below control values. Plasma FSH levels were also lower in the oxytocin-treated animals. Intratesticular oxytocin treatment did not affect LH or oxytocin concentrations in the plasma, epididymal sperm counts or the number of Leydig cells in the testis. Empty Accurel devices had no effect on testicular morphology. This study provides the first evidence that oxytocin in vivo can modify steroidogenesis in the testis.