Lawrence A. Frohman

Impaired Growth Hormone Responses to Growth Hormone–Releasing Factor in Obesity: A Pituitary Defect Reversed with Weight Reduction

To investigate whether the impaired growth hormone secretion associated with obesity is a result of a hypothalamic or a pituitary disorder and whether it is a cause or a consequence of obesity, we studied plasma growth hormone responses to growth hormone-releasing factor in morbidly obese patients before gastrointestinal surgical therapy, in formerly obese subjects who had lost considerable weight postoperatively, and in non-obese controls. Growth hormone secretion was also assessed in response to insulin-induced hypoglycemia (in seven patients preoperatively and four postoperatively). In patients studied preoperatively, growth hormone responses to growth hormone-releasing factor were markedly impaired (P less than 0.001 as compared with controls), whereas in patients studied postoperatively they were partially restored to normal (P less than 0.05 as compared with those studied preoperatively). Growth hormone responses to insulin-induced hypoglycemia were similarly diminished in obese patients studied before operation (P less than 0.02). The growth hormone response to growth hormone-releasing factor was inversely correlated with the percentage of ideal body weight (P less than 0.01) and directly correlated with the growth hormone response to insulin (P less than 0.01). The impaired responsiveness to growth hormone-releasing factor suggests that the diminished response to insulin hypoglycemia is mediated by an impaired pituitary response to endogenous growth hormone-releasing factor. The reversibility of the defect after weight reduction suggests that it is a consequence rather than a cause of obesity.

Thyroid cancer occurring as a late consequence of head and neck irradiation. Evaluation of 1056 patients

From January 1 to September 30, 1974, we examined 1056 of 5266 subjects (20.1%) who had received therapeutic irradiation primarily for infections and inflammatory disease of the upper respiratory tract at our institution during the 1940s and 1950s. The tonsillar and nasopharyngeal region was the treatment site in 85% of those examined. Palpable nodular thyroid disease was found in 16.5%, and nonpalpable lesions were detected by 99m Tc pertechnetate thyroid imaging in an additional 10.7%, for a prevalence of nodular disease of 27.2%. Operation on 71% with nodular disease revealed thyroid cancer in 33% (60 of 182). Preliminary analysis for potential risk factors suggests a correlation between radiation exposure and the presence of thyroid nodules (P less than 0.001). These findings indicate that nodular thyroid disease, both benign and malignant, continues as a major health problem for at least 35 years in exposed subjects.

Effect of vagotomy and vagal stimulation on insulin secretion.

The influence of the vagus nerve on insulin secretion in the dog has been confirmed by studies involving both vagotomy and vagal stimulation. Following vagotomy, a fall in portal vein insulin levels occurs. Following stimulation of both the right and left vagus, insulin levels rise abruptly, peak within five minutes and rapidly return to baseline levels. A small rise in blood glucose, which occurs simultaneously, cannot be blocked by phentolamine, an alpha-adrenergic blocking agent. When given alone, phentolamine stimulates insulin secretion. Atropine inhibits both the glucose and insulin rises following vagal stimulation. Only a portion of releasable insulin appears to be under vagal control. Glucose mediated insulin release and net glucose utilization are not significantly affected by vagotomy.

Ovarian function in chronic renal failure: evidence suggesting hypothalamic anovulation.

The pathogenesis of ovarian dysfunction in uremia was evaluated in 24 patients by measurements of plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone, prolactin, estradiol, and progesterone basally and after clomiphene, ethinyl estradiol, and bromocriptine. In the 17 premenopausal women, levels of plasma estradiol, progesterone, and FSH were comparable to those found in normal women during the follicular phase of the ovarian cycle; plasma luteinizing hormone was slightly elevated. In most patients, there was an absence of cyclicity. After clomiphene, plasma levels of luteinizing hormone, FSH, and estradiol rose; after ethinyl estradiol, plasma luteinizing hormone levels failed to increase. In seven postmenopausal patients, plasma estradiol was undetectable and gonadotropin levels were markedly elevated. Although plasma prolactin was generally elevated, suppression of prolactin with bromocriptine resulted in resumption of ovulation in only one patient; the other 2 remained amenorrheic. In uremic women, the continued secretion of estrogen, the rise of plasma levels of luteinizing hormone, FSH, and estradiol after clomiphene, and the elevated gonadotropin levels during menopause suggest that the negative estradiol feedback, the tonic gonadotropin secretion, and the pituitary ovarian axis were normal. The positive estradiol feedback associated with cyclic release of luteinizing hormone, however, was impaired as indicated by the prevalence of acyclicity and the failure of luteinizing hormone levels, to rise after ethinyl estradiol.

Dipeptidylpeptidase IV and trypsin-like enzymatic degradation of human growth hormone-releasing hormone in plasma.

The plasma enzyme responsible for primary proteolytic cleavage of growth hormone-releasing hormone (GRH) at the 2-3 amino acid bond was characterized. Native GRH[GRH(1-44)-NH2 and GRH(1-40)-OH], and COOH-terminally shortened fragments [GRH(1-32)-NH2 and GRH(1-29)-NH2] were rapidly cleaved, while GRH(2-32)-NH2 was not degraded at this site. Moreover, degradation to GRH(3-44)-NH2 was unaffected by an aminopeptidase inhibitor, indicating that this metabolite was generated from a single step cleavage by a dipeptidylpeptidase (DPP) rather than sequential aminopeptidase cleavages. Conversion to GRH(3-44)-NH2 was blocked by diprotin A, a DPP type IV (DPP IV) competitive inhibitor. D-Amino acid substitution at either position 1 or 2 also prevented hydrolysis, characteristic of DPP IV. Analysis of endogenous plasma GRH immunoreactivity from a human GRH transgenic pig revealed that the major peak coeluted with GRH(3-44)-NH2. Native GRH exhibited trypsin-like degradation at the 11-12 position but cleavage at the 12-13 site occurred only with GRH(1-32)-NH2 and GRH(1-29)-NH2. Formation of these metabolites was independent of prior DPP IV hydrolysis but was greatly reduced by trypsin inhibitors. Evaluation of plasma stability of potential GRH super analogues, designed to resist degradation by these enzymes, confirmed that GRH degradation in plasma occurs primarily by DPP IV, and to a lesser extent by trypsin-like enzyme(s).

Measurement of growth hormone-releasing hormone and somatostatin in hypothalamic-portal plasma of unanesthetized sheep. Spontaneous secretion and response to insulin-induced hypoglycemia.

To elucidate the role of growth hormone (GH)-releasing hormone (GRH) and somatostatin (SRIH) in the regulation of the growth hormone (GH) secretory pattern, we collected portal blood from five unanesthetized ovariectomized ewes for repeated measurements of GRH and SRIH simultaneous with those of peripheral GH. Hormones were measured at 10-min intervals for 5.5 h and their interrelationships analyzed. Mean portal GRH was 20.4 +/- 6.7 (SD) pg/ml and the estimated overall secretion rate was 13 pg/min. GRH secretion was pulsatile with peaks of 25-40 pg/ml and a mean pulse interval of 71 min. Mean portal SRIH was 72 +/- 33 pg/ml and the estimated overall secretion rate was 32 pg/min. SRIH secretion was also pulsatile with peaks of 65-160 pg/ml and a mean pulse interval of 54 min. The GH pulse interval was 62 min. A significant association was present between GRH and GH secretory peaks though not between GRH and SRIH or SRIH and GH. Insulin hypoglycemia resulted in a rapid and brief stimulation of SRIH secretion followed by a decline in GH levels. No effect was observed on GRH secretion until 90 min, when a slight increase occurred. The results suggest (a) the presence of an independent neural rhythmicity of GRH and SRIH secretion with a primary role of GRH in determining pulsatile GRH secretion, and (b) that the inhibitory effects of insulin hypoglycemia on GH in this species are attributable to a combination of enhanced SRIH secretion and possibly other factors, though without significant inhibition of GRH.

Rapid enzymatic degradation of growth hormone-releasing hormone by plasma in vitro and in vivo to a biologically inactive product cleaved at the NH2 terminus.

The effect of plasma on degradation of human growth hormone-releasing hormone (GRH) was examined in vitro and in vivo using high performance liquid chromatography (HPLC), radioimmunoassay (RIA), and bioassay. When GRH(1-44)-NH2 was incubated with human plasma, the t1/2 of total GRH immunoreactivity was 63 min (RIA). However, HPLC revealed a more rapid disappearance (t1/2, 17 min) of GRH(1-44)-NH2 that was associated with the appearance of a less hydrophobic but relatively stable peptide that was fully immunoreactive. Sequence analysis indicated its structure to be GRH(3-44)-NH2. Identity was also confirmed by co-elution of purified and synthetic peptides on HPLC. Biologic activity of GRH(3-44)-NH2 was less than 10(-3) that of GRH(1-44)-NH2. After intravenous injection of GRH(1-44)-NH2 in normal subjects, a plasma immunoreactive peak with HPLC retention comparable to GRH(3-44)-NH2 was detected within 1 min and the t1/2 of GRH(1-44)-NH2 (HPLC) was 6.8 min. The results provide evidence for GRH inactivation by a plasma dipeptidylaminopeptidase that could limit its effect on the pituitary.

Partial purification and characterization of a peptide with growth hormone-releasing activity from extrapituitary tumors in patients with acromegaly.

Growth hormone (GH)-releasing activity has been detected in extracts of carcinoid and pancreatic islet tumors from three patients with GH-secreting pituitary tumors and acromegaly. Bioactivity was demonstrated in 2 N acetic acid extracts of the tumors using dispersed rat adenohypophyseal cells in primary monolayer culture and a rat anterior pituitary perifusion system. The GH-releasing effect was dose responsive and the greatest activity was present in the pancreatic islet tumor. Small amounts of activity were also found in two other tumors (carcinoid and small cell carcinoma of lung) unassociated with GH hypersecretion. Each of the tumors contained somatostatin-like immunoreactivity but the levels did not correlate with the net biologic expression of the tumor. Sephadex G-75 gel filtration indicated the GH-releasing activity to have an apparent molecular size of slightly greater than 6,000 daltons. The GH-releasing activity was adsorbed onto DEAE-cellulose at neutral pH and low ionic strength, from which it could be eluted by increasing ionic strength. The GH-releasing activity was further purified by high pressure liquid chromatography using an acetonitrile gradient on a cyanopropyl column to yield a preparation that was active at 40 ng protein/ml. Partially purified GH-releasing activity, from which most of the bioactive somatostatin had been removed, increased GH release by pituitary monolayer cultures to five times base line. Enzymatic hydrolysis studies revealed that the GH-releasing activity was resistant to carboxypeptidase, leucine-aminopeptidase, and pyroglutamate-amino-peptidase but was destroyed by trypsin and chymotrypsin, indicating that internal lysine and/or arginine and aromatic amino acid residues are required for biologic activity and that the NH2-terminus and CO9H-terminus are either blocked or not essential. The results provide an explanation for the presence of GH-secreting tumors in some patients with the multiple endocrine neoplasia syndrome, type I, and warrant the addition of GH-releasing activity to the growing list of hormones secreted by tumors of amine precursor uptake and decarboxylation cell types.

Salivary Gland Neoplasms as a Late Consequence of Head and Neck Irradiation

An increased occurrence of salivary tumors was observed in 1922 patients who received radiation to the tonsils and nasopharynx. Twenty-seven tumors, 19 benign and eight malignant, were found in this group as compared with an expected 0.2 malignant and less than 1 benign tumor. The latent period between the initial radiation treatment and diagnosis ranged from 7 to 32 years. After the first 15 years the incidence (77 cases/10(5) subjects/year) has remained constant and shows no indication of declining. Continued observation for salivary gland tumors is therefore indicated for subjects who received childhood irradiation.

Incidence, prevalence and characteristics of radiation-induced thyroid tumors

Abstract A population of 5,266 persons were known to be at risk for the development of thyroid neoplasms as a result of prior head and neck irradiation for benign conditions received at our institution. We contacted 2,578 (49.0 per cent) of these persons of whom we examined 1,476 (28.0 per cent) and received follow-up data on 713 (13.5 per cent). Prior to the onset of our recall program, 209 persons had had thyroid surgery (9.4 per cent of those with adequate follow-up data). The incidence of thyroid operations after the initial radiation treatment was low for 10 years and then increased continuously for at least 25 years. The incidence of carcinoma found at operations performed before the recall program and after was similar (37.1 per cent before versus 36.2 per cent after). This high percentage, which was not changed by the follow-up and examination program, supports the conclusion that the probability of finding thyroid cancer in a nodular gland is increased in irradiated patients. No risk factors were found in irradiated subjects that distinguished between malignant and benign disease. Of 50 patients who were examined and who had a history of prior thyroid surgery, 18 (36 per cent) had evidence of new thyroid tumors. In this limited group, thyroid suppressive therapy appeared to prevent recurrences. However, a larger trial to assess the value of thyroid suppression is still warranted. One subject is known to have died of thyroid cancer.