Anterior pituitary dysfunction in patients with chronic renal failure treated by hemodialysis or continuous ambulatory peritoneal dialysis

Pituitary Adrenal Responsiveness to Corticotropin-Releasing Hormone in Chronic Uremic Patients

We investigated the effect of exogenous ovine corticotropin-releasing hormone (oCRH) on plasma levels of adrenocorticotropic hormone (ACTH) and cortisol in 24 chronic renal failure patients: 8 nondialysis (NDCRF), 8 on hemodialysis (HD), and 8 on continuous ambulatory peritoneal dialysis (CAPD). In all groups the acute administration of oCRH caused a further increase (less pronounced in NDCRF patients) in the already elevated levels of cortisol. Following oCRH administration, plasma ACTH rose significantly in CAPD patients, but there was a blunted response of the hormone in the NDCRF and HD groups. The patterns of the ACTH and cortisol response in the last two groups, resemble those observed in chronic stress. We conclude that the hypothalamic-pituitary-adrenal axis in chronic uremic patients, retains the ability to respond to exogenous oCRH. Patients on CAPD, however, display a better, identical to normal response, which can be due to less chronic stress andlor to the more effective clearance of uremic toxins.

Role of Growth Hormone Deficiency and Treatment in Chronic Kidney Disease

Malnutrition and inflammation are strong predictors of mortality in advanced kidney disease, especially in patients on renal replacement therapy. The complex relationship between kidney disease, uremia, and malnutrition significantly contributes to the increased morbidity and mortality in this patient population potentially through a relative deficiency in growth hormone (GH). With an approximate 26 million Americans currently affected by some stage of chronic kidney disease and a predicted 750,000 people to be on dialysis by 2020, there is a need to develop innovative strategies aimed at reducing the high mortality seen in dialysis patients. We will review evidence on one such intervention with infusion of recombinant GH to improve the nutritional and inflammatory state, thereby expecting to improve the mortality and morbidity in this patient population.

Systemic illness

Systemic illnesses are associated with alterations in the hypothalamic-pituitary-peripheral hormone axes, which represent part of the adaptive response to stressful events and may be influenced by type and severity of illness and/or pharmacological therapy. The pituitary gland responds to an acute stressful event with two secretory patterns: adrenocorticotropin (ACTH), prolactin (PRL) and growth hormone (GH) levels increase, while luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyrotropin (TSH) levels may either decrease or remain unchanged, associated with a decreased activity of their target organ. In protracted critical illness, there is a uniformly reduced pulsatile secretion of ACTH, TSH, LH, PRL and GH, causing a reduction in serum levels of the respective target-hormones. These adaptations are initially protective; however, if inadequate or excessive they may be dangerous and may contribute to the high morbidity and mortality risk of these patients. There is no consensus regarding the type of approach, as well as the criteria to use to define pituitary axis function in critically ill patients. We here provide a critical approach to pituitary axis evaluation during systemic illness.

Cholinergic modulation of growth hormone responses to growth hormone-releasing hormone in uraemic patients on peritoneal dialysis

BACKGROUND

Hypothalamic cholinergic neurotransmission plays a major role in the regulation of GH secretion. Pyridostigmine, a cholinesterase inhibitor, is able to decrease hypothalamic somatostatinergic tone and release GH in normal subjects. Blockade of muscarinic receptor with pirenzepine blunts the GH release in several clinical situations. However, little information is available on the role played by central cholinergic pathways in GH regulation in uraemic patients.

OBJECTIVE

We aimed to assess GH responses to GHRH after pretreatment with pyridostigmine and pirenzepine in a group of uraemic patients undergoing peritoneal dialysis (PD). GH responses of the patients treated with recombinant human erythropeitin (rhEPO) were compared to patients without treatment.

DESIGN

We studied 14 male patients on PD and nine control subjects. All subjects underwent three endocrine test in random order after an overnight fast. Each subject received GHRH (100 microg, i.v. in bolus at 0 minutes). Sixty minutes before the injection of GHRH subjects were given oral placebo, pyridostigmine (120 mg), or pirenzepine (100 mg).

MEASUREMENTS

Blood samples for GH were collected at -60, 0, 15, 30, 45, 60 and 90 minutes The hormonal secretory responses were studied by a time-averaged (area under the curves, AUC) and time-independent (peak values) analysis.

RESULTS

Baseline GH concentrations were similar in patients and controls. GH responses to placebo plus GHRH were also comparable in patients and controls (peak 26.6 +/- 3.8 vs. 33.2 +/- 4.4 mU/l, AUC 28.2 +/- 3.4 vs. 27.8 +/- 4.6 mU/h/l). Pyridostigmine administration induced a significant potentiation of GH responses to GHRH both in patients (peak 43.2 +/- 5.2 mU/l, AUC 47.6 +/- 6.0 mU/h/l; P < 0.01) and in control subjects (peak 79.2 +/- 8.6 mU/l, AUC 78.0 +/- 9.4 mU/h/l; P < 0.01). However, the increment in GH peak and AUC was significantly (P < 0.05) greater in controls in relation to values found in patients. Pirenzepine administration induced an abolishment of GH release after GHRH stimulation both in PD patients (peak 5.4 +/- 2.6 mU/l, AUC 6.0 +/- 2.4 mU/h/l; P < 0.01) and in healthy controls (peak 3.8 +/- 0.6 mU/l, AUC 4.0 +/- 0.4 mU/h/l; P < 0.05). Responses to pyridostigmine plus GHRH and pirenzepine plus GHRH were similar in patients on chronic therapy with recombinant human erythropeitin and in patients without rhEPO therapy.

CONCLUSION

These results suggest that the cholinergic regulation of GH release is preserved in uraemic patients on peritoneal dialysis. The significantly lower increase in GH response to GHRH induced by pyridostigmine suggests that cholinergic stimulatory tone is attenuated in patients in relation to control subjects. Long-term therapy with rhEPO seems not to affect GH responses to cholinergic stimulation or blockade.

The epidemiology, anatomy, physiology, and treatment of erectile dysfunction in chronic renal failure patients

Erectile dysfunction (ED) is an associated morbidity for men with chronic renal failure. An understanding of the epidemiology, anatomy, physiology, and treatment options for ED can greatly improve the quality of life for men with chronic renal failure. There are psychological and physiological causes for erectile dysfunction. Once the key features leading to the patient's loss of potency have been identified, appropriate treatment plans can be instituted, often with successful outcomes. The purpose of this article is to assist the nephrology interdisciplinary team in the management of ED by reviewing possible causes, available studies, and treatment options for their patients.

Impaired secretion of growth hormone in experimental uremia: relevance of caloric deficiency

To evaluate the impact of uremia and associated caloric restriction on physiologically pulsatile growth hormone (GH) release, we used deconvolution analysis of spontaneous plasma GH profiles in 5/6-nephrectomized male rats (NX, N = 9). Three different normal renal function sham-operated groups were used: rats fed a normal diet ad libitum (SAL, N = 9); NX pair-fed rats (SPF, N = 6); NX rats pair-fed for protein ingestion but calorically supplemented up to the energy intake of SAL (SPF+, N = 8). Severe renal failure was confirmed by much higher (P < 0.001) BUN in NX than sham groups. NX rats were growth retarded as shown by reduced (P < 0.01) weight and length gains as compared with sham animals. Deconvolution analysis (mean +/- SEM) of plasma samples obtained every 10 minutes over 6 hours, and 14 to 16 days after second stage nephrectomy showed that NX rats had a longer GH t(1/2) (17.0 +/- 1.8 vs. 11.6 +/- 0.8 min), less GH mass secreted per burst (48 +/- 15 vs. 95 +/- 16 ng/ml/pulse), lower secretory pulse amplitude (1.9 +/- 0.5 vs. 5.8 +/- 0.9 ng/ml/min), and a reduced total GH secretion (240 +/- 69 vs. 400 +/- 56 ng/ml/6 hr) than SAL rats. Corresponding data were not significantly different between NX and SPF, or between SAL and SPF+ groups. In summary, stunted rats with chronic renal failure exhibit a prolonged GH t(1/2) and suppression of GH secretory pattern burst mass. Control data from rats with normal renal function suggest that the amplitude-specific depression of GH secretion may be attributed, at least in part, to chronic renal failure-associated calorie deficiency.

Serum beta-endorphin in non-dialysed and haemodialysed patients with chronic renal failure

Endogenous opioid peptides play an important role in the pathogenesis of uraemic syndrome. The effect of insulin-induced hypoglycaemia on serum beta-endorphin (BE) concentration was studied in 27 uraemic patients and in 14 healthy subjects. Despite elevated basal BE level, that correlated positively with serum creatinine, uraemic patients showed a normal BE secretory pattern. No differences were found between uraemic patients on conservative and those on haemodialysis treatment. The influence of haemodialysis treatment on BE secretion requires further investigations.

Growth hormone secretion from pituitary cells in chronic renal insufficiency

To examine whether growth hormone (GH) secretion is adversely affected by chronic renal insufficiency (CRI), the GH secretory response of dispersed anterior pituitary cells perifused with GH-releasing hormone (GHRH) was investigated in 5/6 nephrectomized (CRI, N = 18) and sham-operated (N = 18) rats. Two weeks after nephrectomy, during a period of stable uremia, CRI rats had significantly higher serum concentrations (mean +/- SEM) of urea nitrogen and creatinine than sham rats, 16.8 +/- 1.4 mmol/liter (47 +/- 4 mg/dl) and 79.6 +/- 0.0 mumol/liter (0.9 +/- 0.0 mg/dl) versus 6.1 +/- 0.4 mmol/liter (17 +/- 1 mg/dl) and 35.4 +/- 0.0 mumol/liter (0.4 +/- 0.0 mg/dl), respectively (P less than 0.0001). Incremental gains in body weight and nose to tail-tip length of CRI rats over two weeks were also significantly depressed, 53.3 +/- 5.38 g (CRI) versus 87.0 +/- 3.78 g (sham; P less than 0.0001) and 3.2 +/- 0.2 cm (CRI) versus 3.6 +/- 0.1 cm (sham; P less than 0.05). The cumulative food intake as well as food efficiency (g food consumed/g weight gain) were also adversely influenced by the uremic state: food intake 304 +/- 1 g (CRI) versus 397 +/- 6 g (sham; P less than 0.0001) and food efficiency 0.173 +/- 0.013 g/g of weight gain (CRI) versus 0.219 +/- 0.008 g/g of weight gain (sham). No significant difference in GH secretory rate (ng/min/10(7) cells) was found between the uremic and sham animals under basal conditions, 65.2 +/- 2.1 (CRI) and 67.9 +/- 2.2 (sham) or in response to GH-releasing hormone, 282.8 +/- 42.4 (CRI) versus 306.2 +/- 42.6 (sham).(ABSTRACT TRUNCATED AT 250 WORDS)

Disturbance of growth hormone--insulin-like growth factor axis in uraemia. Implications for recombinant human growth hormone treatment

The growth hormone/insulin-like growth factor (IGF) axis is disturbed in uraemia. Elevated plasma growth hormone (GH) levels despite diminished growth suggest GH resistance, which may be due in part to a decreased expression of the growth hormone receptor at the cell membrane. The hepatic production of IGFs under the control of GH is impaired. Furthermore, there is an excess of IGF-binding protein over total IGF as a consequence of reduced renal clearance of low-molecular-weight subunits of the IGF-binding protein (IGF-BP). This results in an absolute (diminished production) and a relative (low bioavailability) deficiency of IGF. Recombinant human growth hormone (rhGH) in doses of 4 IU/m2 per day is able to induce catch-up growth in children with preterminal and terminal renal failure. The growth stimulation of exogenous GH is attributed to its potency to increase the ratio of IGF-I to IGF-BP, followed by a normalization of IGF bioactivity. In renal transplanted children growth is not only disturbed by decreased renal function but also by steroid treatment. Corticosteroids are responsible for catabolism, for suppression of pituitary GH secretion and for inhibition of local production of IGFs. Exogenous rhGH is able to counteract these growth-inhibiting effects. However, it remains to be seen whether long-term GH treatment definitely improves final adult height.