Lack of effect of muscarinic cholinergic blockade on the GH responses to GRF 1-29 and TRH in acromegalic subjects

Thyroid function in early pregnancy. II: Paradoxical growth hormone response to thyrotropin-releasing hormone

A variant of growth hormone (GH) known as human placental growth hormone (hpGH) is found in maternal serum during pregnancy. It is well established that during the second half of normal pregnancy, pituitary GH secretion is suppressed; however, there are no data about maternal GH secretion during the first trimester of pregnancy. The present study reports the response of GH to thyrotropin-releasing hormone (TRH) in eight pregnant women in the trimester of pregnancy (weeks 6-9) who had previously requested voluntary interruption of pregnancy. The TRH test induced a significant paradoxical GH response with a peak of 9.4 +/- 0.5 ng/ml (mean +/- SD) at 30 min and a higher thyroid-stimulating hormone (TSH) response in pregnant women. The increment was observed until 120 min and no response was observed in the control group. These data show the paradoxical response of GH to TRH, a releasing factor to which the hormone does not normally respond. This paradoxical secretion may be due to direct pituitary stimulation and can be explained on the basis of a state of gestational hypothyroidism.

Lack of involvement of the cholinergic mechanism in vasoactive intestinal peptide- and peptide-histidine methionine-induced growth hormone (GH) responses in acromegaly: comparison with the GH responses to thyrotropin-releasing hormone and GH-releasing hormone

We examined whether the cholinergic mechanism is involved in the paradoxical GH responses to vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) in acromegaly. 28 patients with active acromegaly underwent i.v. bolus injections of thyrotropin-releasing hormone (TRH, 500 micrograms), GH-releasing hormone (GHRH, 100 micrograms), VIP (100 micrograms), and PHM (100 micrograms) with or without a prior atropine treatment (1 mg, i.m., 30 min before). Blood samples were collected before and at intervals up to 120 min after the injection, and plasma GH levels were measured. In response to TRH, GHRH, VIP and PHM, 23 (82%), 24 (86%), 13 (46%) and 7 (25%) patients, respectively, responded with a significant GH increase (> 50% and 6 micrograms/l above the basal level). The effect of atropine pretreatment was examined in only these responders to the respective peptides. When the GH responses were estimated by the area under the response curve, the atropine pretreatment was able to significantly suppress the GH response to GHRH, but not to TRH, VIP, or PHM. Although the lack of cholinergic involvement in the TRH-induced GH release in acromegaly is confirmatory to previous reports, the same results with the VIP- and PHM-induced GH release are novel. The present study may suggest that in acromegaly the physiological GH response is mediated by the cholinergic mechanism, but the paradoxical ones are not.

A clinical update on hypothalamic-pituitary control

There is at present an accumulation of data which indicate the importance of stimulatory and inhibitory growth factors in the paracrine, and perhaps autocrine, regulation of anterior pituitary cell growth and function. There may well be several more specific pituitary growth factors which will be identified in the near future. Preliminary data are also emerging concerning the pattern of oncogene expression in human pituitary tumours. It is now necessary to relate growth factor production, oncogene expression and hypothalamic regulation to specific anterior pituitary cell populations and human pituitary adenomas. In the midst of these studies it should not be forgotten that coordinated vascular and supporting tissue growth is also crucial to the normal development and maintenance of anterior pituitary structure and function.

Cholinergic muscarinic receptor blockade with pirenzepine abolishes slow wave sleep-related growth hormone release in normal adult males

Cholinergic pathways play an important role in the regulation of GH secretion from the anterior pituitary gland, and in this study we have investigated whether cholinergic muscarinic receptor blockade with pirenzepine displayed any inhibitory action on slow wave sleep-related GH release in normal subjects. Six adult males (ages 24-37 years) were studied in a randomized order and fasted from 1800 h on each study day. All subjects showed episodes of slow wave sleep on each occasion and this was followed by peaks of GH release when placebo alone was administered (range of GH peaks 4-50 mU/l). In contrast, pirenzepine treatment (100 mg p.o. at 2200 and 2400 h) completely abolished nocturnal GH release in each individual without altering the occurrence of slow wave sleep itself. These data demonstrate clearly that cholinergic muscarinic receptor blockade completely abolishes slow wave sleep-related GH release in normal adult subjects. Because of the striking effects it is reasonable to conclude that acetylcholine plays an important stimulatory role in mediating slow wave sleep-related GH release. This finding may have investigational and therapeutic applications in young patients with Type 1 diabetes mellitus since GH is implicated in some acute metabolic and chronic microvascular complications of this disease.