Hypophysial responses to continuous and intermittent delivery of hypopthalamic gonadotropin-releasing hormone.

In rhesus monkeys with hypothalamic lesions that abolish gonadotropic hormone release by the pituitary gland, the constant infusion of exogenous gonadotropin-releasing hormone (GnRH) fails to restore sustained gonadotropin secretion. In marked contrast, intermittent administration of the synthetic decapeptide once per hour, the physiological frequency of gonadotropin release in the monkeys, reestablishes pituitary gonadotropin secretion. This phenomenon is attributable to the pattern of GnRH delivery rather than to the amounts of this hormone to which the cells of the pituitary are exposed. Moreover, the initiation of continuous GnRH administration in animals with lesions and in which gonadotropin secretion is reestablished by intermittent GnRH replacement can result in a "desensitization" or "down regulation" of the processes responsible for gonadotropin release.

Control of the rhesus monkey menstrual cycle: permissive role of hypothalamic gonadotropin-releasing hormone.

In rhesus monkeys with hypothalamic lesions (which appear to abolish the endogenous production of gonadotropin-releasing hormone), normal ovulatory mestrual cycles were reestablished by an unvarying, long-term replacement regimen consisting of one intravenous pulse of synthetic gonadotropic-releasing hormone per hour. This finding is in accord with the hypothesis that the pattern of pituitary gonadotropin secretion throughout the menstrual cycle (basal secretion interrupted, once every 28 days on the average, by a preovulatory surge) is not directed by alterations in hypothalamic gonadotropin-releasing hormone secretion but by the ebb and flow of ovarian estrogens acting directly on the pituitary gland.

Different patterns of allelic loss (loss of heterozygosity) in recurrent human pituitary tumors provide evidence for multiclonal origins.

Sporadic human pituitary tumors are benign adenomas of monoclonal origin. This implies that they arise from de novo somatic mutation(s) within a single pituitary cell. The availability of original and recurrent/regrown tumors from the same patient allowed testing of the prediction that recurrent/regrown tumors have identical genetic abnormalities as the original tumor sample. We used PCR amplification, from archival slide-extracted DNA, to allelotype microsatellite polymorphisms as an indication of clonality and confirmed this by X chromosome inactivation analysis in samples from women. Tumors from 33 of 49 (67%) patients with two or more specimens showed loss of heterozygosity (LOH) of at least one marker in at least one of their samples. Two patterns of LOH were observed. In pattern A in 14 of 33 (42%) of patients, the LOH pattern of the first tumor was preserved in the second recurrent sample, with some recurrent tumors also showing additional LOH. In these patients, the original and second tumors are presumed to arise from the same original clone with or without progressive accumulation of LOH. In pattern B [19 of 33 (58%) patients], LOH seen in the first tumor was not preserved in the second or subsequent tumors, as evidenced by retention of heterozygosity compared with the first tumor. The simplest explanation is that the second tumor, although still monoclonal, arises from another independently abnormal clone. This was confirmed by X chromosome inactivation analysis in all 11 women where this was informative. These results show that initial and recurrent tumors, of a benign tumor type, are frequently derived from separate independent clones. This suggests that either: (a) more than one abnormal clone is present from the outset though only one dominates; or (b) several clones arise independently at different times. In both scenarios, the initiating event(s) that predisposes to transformation might result in multiclonal hyperplasia, possibly as a consequence of exogenous stimulation.

The sites of action of estradiol and phentolamine in the inhibition of the pulsatile, circhoral discharges of LH in the rhesus monkey (Macaca mulatta).

Pulsatile LH secretion was re-established in ovariectomized monkeys bearing hypothalamic lesions by an intermittent infusion of LHRH. The administration of estradiol to such animals resulted in a prompt cessation of these pulsatile discharges of LH and a resultant decline in the mean plasma concentration of the gonadotropin. The time course of this inhibition of LH secretion was indistinguishable from that observed after estrogen administration to ovariectomized animals with intact nervous systems. In contrast, phentolamine did not interrupt the pulsatile LH discharges occasioned by the hourly administration of exogenous LHRH to the lesioned animals. These results are consistent with the conclusion that the acute negative feedback action of estradiol on circhoral LH release in the monkey is at the level of the pituitary gland, whereas the inhibitory action of phentolamine on this mode of LH secretion is at a neural site.

Frequency and amplitude of gonadotropin-releasing hormone stimulation and gonadotropin secretion in the rhesus monkey.

In adult ovariectomized rhesus monkeys bearing hypothalamic lesions which reduced circulating LH and FSH to undetectable levels, sustained elevated gonadotropin concentrations were reestablished by the intermittent administration of gonadotropin-releasing hormone (GnRH) at the rate of 1 microgram/min for 6 min once every hour. The effects of varying either the frequency or the amplitude of these GnRH pulses on gonadotropin secretion were examined in such animals. Increasing the frequency of GnRH administration from the physiological one pulse per h to two, three, or five pulses h while maintaining a constant infusion rate and pulse duration resulted in gradual declines in plasma gonadotropin concentrations. These declines were most profound at the highest frequencies and the consequence of reduced pituitary responses to individual GnRH pulses. Decreasing the frequency of GnRH pulses from one per h to one every 3 h led to variable declines in plasma LH levels, but circulating FSH invariably rose. Reducing the GnRH infusion rate from 1 to 0.1 mg/min while maintaining constant frequency and pulse duration resulted in abrupt declines in plasma LH and FSH to immeasurable levels, although pulsatile increments in circulating GnRH concentrations without a concomitant reduction in plasma LH concentrations, which remained unchanged. An infusion rate of 0.5 microgram/min resulted in unstable plasma LH and FSH levels. These results demonstrate that changes in the frequency or amplitude of hypophysiotropic stimulation have profound effects on plasma gonadotropin levels as well as on FSH to LH ratios in the circulation. The physiological implications of these observations are discussed.

Development of acromegaly during treatment of hyperprolactinemia with bromocriptine: an unusual acidophil stem cell adenoma.

We present clinical details of a patient with a 20-yr history of amennorhea, a pituitary tumor, elevated PRL levels, and initially undetectable GH. Bromocriptine failed to fully suppress PRL, and there was no tumor shrinkage. Within 7 months of starting bromocriptine treatment, the patient developed clinical and biochemical signs of acromegaly. At surgery, a stem cell adenoma was excised. The mechanisms by which bromocriptine may have resulted in the development of acromegaly in this patient are discussed.

Mortality and cancer incidence in acromegaly: a retrospective cohort study. United Kingdom Acromegaly Study Group.

Patients with acromegaly have a reduced life expectancy, with the accepted causes for premature death being vascular and respiratory disease. Increased mortality from malignant disease has also been reported. We, therefore, performed a multicenter retrospective cohort study of 1362 patients with acromegaly and investigated the relationships of mortality and cancer incidence with GH levels, duration of disease, and age at diagnosis. The overall cancer incidence rate [standardized incidence ratio, 0.76; 95% confidence interval (CI), 0.60-0.95] was lower than that in the general population of the United Kingdom, and there was no significant increase in site-specific cancer incidence rates. The overall cancer mortality rate was not increased, but the colon cancer mortality rate (standardized mortality ratio, 2.47; 95% CI, 1.31-4.22) was higher than expected. Mortality rates due to colon cancer, all malignant disease, cardiovascular disease and overall mortality were increased with higher posttreatment GH levels (P for trends, <0.02, <0.05, <0.02, and <0.0001). The overall mortality rate in patients with acromegaly with posttreatment GH levels less than 2.5 ng/mL (5 mU/L) was comparable to that in the general population of the United Kingdom (standardized mortality ratio, 1.10; 95% CI, 0.89-1.35). We conclude that high posttreatment GH levels are associated with an increased overall mortality rate and increased mortality rates due to colon cancer, cardiovascular disease, and all malignant disease. Posttreatment GH levels less than 2.5 ng/mL (5 mU/L) result in an overall mortality rate similar to that in the general population.

The effects of insulin-like growth factor-1 on plasminogen activator inhibitor-1 synthesis and secretion: results from in vitro and in vivo studies.

In vitro studies have shown that insulin and IGF-1 releases the fibrinolytic inhibitor plasminogen activator inhibitor-1 (PAI-1) from cells of hepatic origin. To investigate the effects of IGF-1 on fibrinolysis: 1) cultured hepatoma cells were grown in the presence of IGF-1 and media collected for secreted PAI-1 and cells probed for PAI-1 mRNA, 2) 8 hypopituitary patients were treated with recombinant human growth hormone (rhGH) and 3) 5 type 2 diabetic patients were treated with recombinant human IGF-1 (rhIGF-1). Treatment of Hep G2 cells with IGF-1 (1000 ng/ml) increased secretion of PAI-1 from a median value of 80 ng/10(6) cells (range 21-91) to 144 ng/10(6) cells (range 128-169) after 24 h (p < 0.01). Synthesis of PAI-1 mRNA increased in a similar fashion. Treatment of hypopituitary patients with rhGH led to an increase in circulating IGF-1 from a mean value of 166 (range 41-324) ng/ml at baseline to 322 (77-575) ng/ml at 4 weeks and 259 (104-533) ng/ml after 8 weeks (p < 0.02). Despite this, no changes in circulating PAI-1 or fibrinolysis occurred. Type II diabetic patients treated with rhIGF-1 showed an increase in circulating IGF-1 from a mean value of 120 ng/ml (range 109-196), at baseline to 823 ng/ml (585-894) after 5 days. This also was not associated with changes in circulating PAI-1 or in fibrinolysis. The results confirm that IGF-1 induces the synthesis of PAI-1 in Hep G2 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of thyrotrophin secretion by negative feedback of tri-iodothyronine on the hypothalamus.

Bilateral injections of tri-iodothyronine (T3, 2 ng in 2 microliter artificial cerebrospinal fluid, CSF) were made into the hypothalami of 15 hypothyroid rhesus monkeys (Macaca mulatta) prepared with chronically implanted intrahypothalamic cannulae. In 29 out of 96 such injections, the concentration of thyrotrophin (TSH) in the plasma fell rapidly by more than 30% and returned to the basal value over the succeeding 48 h, in 13 experiments the fall was 20-30% and in the remaining 54 experiments the level of TSH was unaltered. With [125I]T3, the extent of diffusion of T3 through the hypothalamus in these experiments was shown to be very limited. The hypothalamic injection sites were subsequently identified histologically and it was found that in those experiments in which the level of TSH in the plasma had fallen, T3 had been injected into either the dorsomedial nucleus or the lateral hypothalamic area extending into the preoptic region. Injection of artificial CSF alone into these areas of the hypothalamus did not affect the concentration of TSH. Direct intrapituitary injections of T3 (4 ng) resulted in small and inconstant changes in the concentration of TSH in the plasma and injections of T3 (400 ng) into the third ventricle were without any effect. These experiments demonstrate that T3 can rapidly inhibit the secretion of TSH by a direct action upon defined parts of the hypothalamus.

Response of luteinizing hormone from columns of dispersed rat pituitary cells to a highly potent analogue of luteinizing hormone releasing hormone.

The response of LH from a perfused column of dispersed rat anterior pituitary cells to LH releasing hormone (LH-RH) and the analogue, D-Ser(But)6-desGly10-Proethylamide9-LH-RH (Hoe 766), was investigated. Dose-response curves showed non-parallelism between LH-RH and the analogue. but it was evident that the analogue was considerably more potent. After a single pulse of LH-RH, LH output returned to basal values in 8 min; this was prolonged to 20 min in the case of the analogue. During this 20 min the cells were refractory to pulses of LH-RH but pulses of the analogue maintained output of LH. During constant-dose perfusion with either synthetic LH-RH or the analogue, output of LH rapidly reached a peak and then gradually fell over several hours to approach baseline values. However, a pulse of 50 mmol potassium chloride/l was still able to release LH at this time. The data are consistent with the view that this analogue of LH-RH is highly potent and is strongly bound by the LH-RH receptor. Furthermore, since it desensitizes the LH-RH receptor, it appears that continued turnover of either LH-RH or the analogue at the receptor is necessary for output of LH to be maintained.

Octreotide treatment increases exercise capacity in patients with acromegaly.

This prospective study was conducted to determine the effect of Octreotide treatment on cardiovascular function in patients with active acromegaly. Ten acromegalic patients who failed to suppress growth hormone (GH) to < 5 mU/l during a 2 h oral glucose tolerance test were treated with 100 micrograms of Octreotide subcutaneously three times daily for 2 months, followed by 200 micrograms three times daily if the mean GH level was > 5 mU/l, for a total of 1 year. All patients had GH and insulin-like growth factor I (IGF-I) estimation, ejection fraction determined by Echocardiogram and multigated image acquisition scan, electrocardiogram (ECG), exercise ECG, 24-h ECG and chest x-ray. At 6 and 12 months, both GH and IGF-I were reduced but ECG, heart size and ejection fraction were unchanged. The patients improved symptomatically and had significant reduction in resting heart rate and increase in weight. Exercise time (mean +/- SD) increased from 637 +/- 137s at baseline to 787 +/- 101s at 1 year (p < 0.01) and work done increased from 9 +/- 3.3 to 11.9 +/- 2.7 metabolic equivalents (p < 0.001). We conclude that the decrease in GH and IGF-I following Octreotide treatment of acromegaly is accompanied by decreased heart rate and increased exercise capacity despite an unchanged ejection fraction.

Bilateral sequential inferior petrosal sinus sampling with corticotrophin-releasing hormone stimulation in the diagnosis of Cushing's disease.

OBJECTIVE: The demonstration of a central to peripheral ACTH gradient in a hypercortisolaemic patient is diagnostic of Cushing's disease. We tried to determine whether single blood samples for ACTH obtained sequentially from each of the inferior petrosal sinuses following human corticotrophin-releasing hormone (hCRH) stimulation can reliably establish such a gradient. DESIGN: Prospective study. PATIENTS: Seventeen patients with clinical and biochemical features of Cushing's syndrome. METHODS: After the administration of hCRH, the patients underwent bilateral sequential inferior petrosal sinus sampling, with a single blood sample obtained from each of the inferior petrosal sinuses sequentially, along with a peripheral venous sample. The petrosal sinus catheter was withdrawn immediately after obtaining a blood sample. Patients did not require indwelling catheters in the petrosal sinuses, nor heparinisation. RESULTS: Bilateral sequential inferior petrosal sinus sampling correctly identified a pituitary source of ACTH, as shown by a central to peripheral ACTH ratio >2, in all patients in whom the procedure was successfully carried out. All patients underwent transsphenoidal pituitary surgery resulting in remission. CONCLUSIONS: The simplified method of inferior petrosal sinus sampling, using a single sequential sample from each of the inferior petrosal sinuses, following initial hCRH stimulation, is as accurate as the more complex test using multiple bilateral simultaneous inferior petrosal sinus samples. It avoids the use of indwelling cerebral venous catheters and is therefore unlikely to cause brain stem damage.

Studies on the accessibility of prolactin and growth hormone to brain: effect of opiate agonists on hormone levels in serial, simultaneous plasma and cerebrospinal fluid samples in the rhesus monkey.

The accessibility of prolactin and growth hormone to the cerebrospinal fluid (CSF) was investigated in rhesus monkeys fitted with reservoirs connected to catheters placed in the fourth ventricle. Simultaneous blood and CSF samples were collected after opiate agonists. There was a brisk, marked rise in plasma prolactin following i.v. morphine sulphate which was followed by a slower, lesser rise in CSF prolactin. After i.v. D-Ala2,MePhe4,Met-O-(ol)-enkephalin (DAMME, FK 33-824, Sandoz) two animals responded similarly but the third showed a much smaller plasma and absent CSF response. Growth hormone showed inconsistent plasma patterns after morphine but a late rise following DAMME; however, CSF growth hormone did not change. Infusion of exogenous human prolactin produced plasma and CSF prolactin levels of similar magnitude and time-course as following opiate agonists. Infusions of larger amounts of purified human growth hormone greatly elevated plasma levels but only led to modest increases in CSF growth hormone. It is concluded that prolactin has relatively ready access to CSF, especially in comparison to growth hormone. The possible significance and mechanisms are discussed.

Growth hormone response to diazepam, clonidine and glucagon in patients with epilepsy.

The differing actions of phenytoin, carbamazepine and sodium valproate on growth hormone release were studied in 20 patients with recently diagnosed epilepsy using diazepam, clonidine and glucagon as stimulatory tests of growth hormone response. The results are compared with the growth hormone response obtained pre treatment, and those from 20 control patients and 11 patients with chronic treated epilepsy. There was a reduction in growth hormone response to diazepam in both treated and untreated patients with epilepsy compared to controls. Treatment with phenytoin resulted in a significant increase in growth hormone release after diazepam and glucagon, whilst sodium valproate reduced the growth hormone response to diazepam.

Prolonged pulsatile release of gonadotropin-releasing hormone from the guinea pig hypothalamus in vitro.

The sexually mature mammal secretes luteinizing hormone in a pulsatile fashion. This is presumed to depend on the intermittent release of hypothalamic gonadotropin- releasing hormone (GnRH). The isolated guinea pig hypothalamus has been studied because, in this species, as in primates, the pulse generator appears to reside within the medial basal hypothalamus. The basal 2 mm of guinea pig hypothalami were rapidly removed and perifused at 37 degrees C with Krebs-Ringer solution containing 20 mM bacitracin gassed with 95% O2, 5% CO2. The eluates were sampled at 15 and 5 min intervals and pulsatile patterns of GnRH were consistently observed for periods up to 72 h. There was no difference in GnRH levels from hypothalami of intact and ovariectomized animals. Simultaneous measurement of TRH and somatostatin disclosed independent pulses of both neurohormones which did not coincide with GnRH, indicating that the peaks were secretory episodes not artefacts generated by varying perifusion rates. The hypothalami disclosed no histologic evidence of necrosis when examined after 20 h perifusion.