Pituitary Venous Blood Research Articles

Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH in the normal stallion in the breeding season.

Pituitary venous blood was collected by a painless nonsurgical cannulation method from five ambulatory stallions at 5-min intervals for 5-6 h during the breeding season. In four adult stallions, statistical analysis showed that pulses of gonadotrophin-releasing hormone (GnRH) and LH were coincident (P less than 0.01), as were pulses of FSH and LH (P less than 0.05). Furthermore, the patterns of changes in concentration of FSH and LH were highly correlated in each of the four stallions. However, seemingly ineffective pulses of GnRH were also observed, with 28% of GnRH pulses failing to induce a significant gonadotrophin pulse. In the four adult stallions the amplitude of pituitary venous gonadotrophin pulses varied markedly but no correlation with GnRH pulse amplitude was observed. Peak secretion of FSH, but not LH, during pulses was correlated with the length of the interpulse interval. Consequently, the ratio of FSH to LH during peaks was least (P less than 0.02) when the interpulse interval was 30 min or less. Thus, differential FSH and LH secretion was achieved within a constant steroid milieu. Two stallions had regular contact with oestrous mares, and in these horses the secretion of GnRH and gonadotrophins occurred almost continuously with rapid, rhythmic pulses superimposed upon a tonic background. Mean (+/- S.D.) interval between GnRH pulses was 31.4 +/- 9.8 min and 27.7 +/- 10.1 min. This secretory pattern was not observed in the two stallions which had infrequent contact with oestrous mares, although the small numbers precluded statistical testing of this apparent difference. No GnRH pulses were observed in one of these stallions, while in the other mean (+/- S.D.) GnRH pulse interval was 45.0 +/- 48.7 min, the large variance being partly due to rapid pulses during a period in which the stallion teased mares. The fifth stallion was pubertal, and GnRH and LH secretion occurred in 15 and 0% of samples respectively, while low levels of FSH secretion were observed in 37% of samples and jugular testosterone levels were immeasurably low. We conclude that there is a statistically significant synchrony between pulses of GnRH, LH and FSH in the pituitary venous blood of stallions. Furthermore, decreasing intervals between gonadotrophin pulses result in a significant reduction in secretion of FSH but not LH.

Effect of isolation stress on concentrations of arginine vasopressin, alpha-melanocyte-stimulating hormone and ACTH in the pituitary venous effluent of the normal horse.

A non-surgical, non-stressful technique was used for collection of pituitary venous blood from five conscious horses every minute for two 10-min periods before and during isolation from the herd, which caused a predictable, yet humane and physiological, emotional stress. Pituitary blood was also sampled every 5 min for two approximately 90-min periods before and after isolation, while jugular blood was sampled every 15 min throughout the experiment. During isolation, all horses became agitated, hyperventilating and sweating. Packed red cell volume increased, as did pituitary venous concentrations of adrenaline (mean +/- S.E.M. concentration before isolation, 621.5 +/- 112.3 pmol/l; peak during isolation, 2665.4 +/- 869.8 pmol/l; P less than 0.05) and noradrenaline (before, 871.8 +/- 111.8 pmol/l; peak, 2726.1 +/- 547.4 pmol/l; P less than 0.02). Concentrations of arginine vasopressin (AVP) were higher in pituitary venous but not in jugular blood during isolation than during the preceding 10-min period (P less than 0.05). Although AVP secretion increased in all horses, in three of the five it rose dramatically in the first minute of isolation to 25.7 (horse 1), 13.6 (horse 4) and 145.1 (horse 5) times the level in the last sample collected before isolation. Mean pituitary venous concentrations of ACTH and alpha-MSH increased during isolation in the three horses which had large increases in AVP secretion, but, overall, stress did not significantly affect ACTH or alpha-MSH secretion. Similarly, mean jugular cortisol levels were not significantly altered by isolation. However, the magnitudes of ACTH, AVP and alpha-MSH responses to isolation were negatively correlated with the jugular cortisol level before isolation. The changes in pituitary venous concentrations of ACTH and AVP were synchronous under resting conditions, whether samples were collected at intervals of 1 (P less than 0.01) or 5 (P less than 0.005) min; however, this synchrony was lost during isolation. The changes in pituitary venous concentrations of ACTH and alpha-MSH were synchronous both at rest (P less than 0.025 for 1-min sampling, P less than 0.01 for 5-min sampling) and during isolation (P less than 0.01). We conclude that isolation stress increases AVP secretion and may alter the temporal relationship between pituitary venous concentrations of AVP and ACTH. Furthermore, the magnitude of the responses of AVP, ACTH and alpha-MSH to isolation is significantly affected by the prevailing cortisol level.

Usefulness of inferior petrosal sinus venous endocrine markers in Cushing's disease.

Bilateral and simultaneous sampling of the inferior petrosal sinuses in patients with Cushing's disease has been used to establish the presence and laterality of adrenocorticotropic hormone (ACTH)-producing microadenomas prior to transsphenoidal surgery. Successful preoperative lateralization depends upon equivalent dilution of pituitary venous blood on the two sides since samples which are diluted by unequal amounts of non-pituitary blood may lead to erroneous results. To assure valid sampling results, the use of other pituitary hormones, measured simultaneously, has been proposed to correct the ACTH concentrations from the inferior petrosal sinuses against unequal dilution by non-pituitary venous blood. This proposal presumes that ACTH-secreting microadenomas will not cause unequal delivery of the other pituitary hormones into the two inferior petrosal sinuses. The inferior petrosal sinus concentrations of prolactin (PRL), thyrotropin (TSH), and the alpha subunit of human chorionic gonadotropin (alpha-HCG) were evaluated as indicators of pituitary venous blood dilution in 11 patients with Cushing's disease. Four patients with ectopic ACTH syndrome served as controls. Blood was withdrawn simultaneously from catheters in both inferior petrosal sinuses and from a peripheral vein for measurement of ACTH, PRL, TSH, and alpha-HCG. The ACTH concentrations were then corrected for dilution by non-pituitary blood by dividing the ACTH concentration from each side by the ratio of the inferior petrosal sinus to peripheral blood concentrations of PRL, TSH, and alpha-HCG for that side. At surgery, all 11 patients had ACTH-secreting microadenomas on the side predicted by the uncorrected ACTH concentrations. However, in three patients the corrected ACTH values would have led to erroneous results. Among the 18 sets of corrected inferior petrosal sinus measurements in these three patients, the corrected ACTH values failed to show an inferior petrosal sinus gradient in six and localized the tumor to the side opposite the adenoma in four. Incorrect lateralization was obtained with each of the hormones (PRL, TSH, and alpha-HCG) used for correction. Furthermore, the ipsilateral (side of tumor)-to-contralateral inferior petrosal sinus gradient of ACTH in patients with Cushing's disease was generally paralleled by a significant inferior petrosal sinus gradient of PRL, TSH, and alpha-HCG to the side of the tumor, whereas patients with the ectopic ACTH syndrome tended not to exhibit lateralizing (side-to-side) gradients.(ABSTRACT TRUNCATED AT 400 WORDS)

Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare.

We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae and all mares ovulated, showing that the procedure did not affect the reproductive axis. In all pituitary-cannulated mares the secretion of gonadotrophin-releasing hormone (GnRH), FSH and LH occurred almost continuously with broad, concurrent pulses of the three hormones superimposed upon this tonic background. Only 9% of the GnRH pulses appeared to be ineffective in inducing a rise in gonadotrophin levels. When measured in pituitary blood, gonadotrophin pulse frequency varied from 0.45 pulses/h early in the LH surge to 1.87 pulses/h at the time of ovulation. In contrast, mean pulse frequency measured in jugular blood did not exceed 1 pulse/h throughout the periovulatory period in cannulated or non-cannulated mares. The low amplitude of jugular pulses (less than 50% fractional increase) may have caused problems in identifying the pulses. In the two mares in which pituitary venous blood was sampled during more than one period before ovulation, GnRH secretion tended to be lower on the day of ovulation (day 0) than earlier in oestrus (ratio day 0:day -1; mare WV = 0.58, mare LS = 0.66), whereas LH secretion rate was higher on the day of ovulation (ratio day 0:day -1; mare WV = 1.54, mare LS = 6.68). These studies show that the painless and non-invasive collection of pituitary venous blood, which is possible only in horses, can provide a useful tool for studying hypothalamic-pituitary interactions under completely physiological conditions.

Transoral, transsphenoidal microsurgical exposure of the pituitary gland and infundibulum in the rhesus monkey

A transoral, transsphenoidal microsurgical technique for exposing the pituitary stalk and gland of the rhesus monkey is described and illustrated. The technique has proved to be a safe and practical method for performing a variety of pituitary operations in a total of 37 animals. The procedures have included complete hypophysectomy, posterior lobe resection, pituitary stalk section, collection of portal venous blood, collection of pituitary venous blood, and placement of lessions in the organum vasculosum of the lamina terminalis.

PROGESTERONE REGULATION OF THE PRODUCTION AND RELEASE OF PITUITARY GONADOTROPHINS IN THE GONADECTOMIZED SHEEP.

One preliminary study and 3 experiments were conducted with gonadectomized male sheep to obtain information on the influence of progesterone administration on the pituitary production and release of gonadotrophic principles. Sequential collections of pituitaries and cavernous sinus blood (pituitary venous blood) were made from progesterone-treated animals, and aliquots of both were bio-assayed in immature, hypophysectomized female rats. The results showed that increased amounts of gonadotrophic hormones were released into the blood stream on the 5th and 6th days of treatment with 20 mg of progesterone daily and again at approximately the same time interval following withdrawal of treatment. Similar increases in the plasma titer were observed on the 6th and 10th day following a single 500 mg injection of progesterone. In some of the experiments in which progesterone was administered daily, smaller increases in the plasma titer were apparent on other days during and following the administration of progester...