The influence of portacaval anastomosis on gonadal and anterior pituitary hormones in a rat model standardized for gender, food intake, and time after surgery

Influence of hypophysectomy, ovariectomy and gonadectomy on postoperative hypersensitivity in rats

Surgical procedures lead to profound and sustained (up to 1–2 weeks) activation of the pituitary gland, resulting in changes in endocrine function. Questions remain on whether activation of the pituitary influences the threshold and development time-course of postoperative pain. To address these questions, we evaluated postoperative hypersensitivity in female and male rats with ablated pituitary and gonadal hormone productions via hypophysectomy, ovariectomy and gonadectomy, respectively. Plantar incision, a model of acute postoperative pain, or sham operation was performed on rat hind paws. Hypophysectomy, ovariectomy and gonadectomy were achieved by surgical disconnection of pituitary, ovaries and testicles, respectively. Postoperative thermal and mechanical hypersensitivity were monitored for 7 days post incision. Hypophysectomy on female and male rats produced statistically similar thermal and mechanical postoperative hypersensitivity thresholds and time-courses as compared to intact estrous female and male rats. Moreover, ovariectomy and gonadectomy did not significantly change postoperative hypersensitivity observed in control female and male animals. Our experiments demonstrate that hypophysectomy, ovariectomy and gonadectomy do not significantly impact postoperative hypersensitivity observed in normal female and male animals. These data suggest that surgery-induced changes in the endocrine system via activation of pituitary and subsequently gonadal tissues have little impact on the threshold and development of postoperative pain in female and male rats.

Gastric estrogen increases pituitary estrogen receptor α and prolactin mRNAs during the different pathological conditions of the liver

Mammalian liver is an estrogen-responsive tissue mediated by hepatic estrogen receptors. Although Ueyama et al. (Endocrinology 143:3162-3170, 2002) have reported the presence of aromatase and active production of gastric 17β-estradiol in parietal cells, there are a few studies on gastric 17β-estradiol exploring the relationship between gastro-hepato function and the gastro-pituitary-gonadal axis. The alteration of gastric 17β-estradiol flow into the systemic circulation by portal vein ligation (PVL) or partial hepatectomy (PH), and the effect of gastric 17β-estradiol on the pituitary function was investigated. In the PVL rats, arterial 17β-estradiol increased 9.5 times that of controls on day 3, and gradually decreased near to control levels in the portal vein by 4 weeks, which was still 5 times higher than those in the arteries of the control rats. In the PH rats, arterial 17β-estradiol increased 2 times that of controls on day 3, and gradually decreased to the control levels. Regeneration and growth of the liver remnants were observed about 2 weeks after PH. In the PVL and PH animals, pituitary ERα and prolactin mRNAs levels increased, positively correlating with an increase of arterial 17β-estradiol levels. Both reduced LHβ mRNA. It is apparent that hepatic dysfunction causes changes in gastric 17β-estradiol levels in the systemic circulation; and that elevated gastric 17β-estradiol affects pituitary function(s). This data suggest that gastric 17β-estradiol has a pivotal role in the regulation of the gastro-hepato-pituitary axis.

Altered expression of genes regulating skeletal muscle mass in the portacaval anastomosis rat

We examined the temporal relationship between portacaval anastomosis (PCA), weight gain, changes in skeletal muscle mass and molecular markers of protein synthesis, protein breakdown, and satellite cell proliferation and differentiation. Male Sprague-Dawley rats with end to side PCA (n=24) were compared with sham-operated pair-fed rats (n=24). Whole body weight, lean body mass, and forelimb grip strength were determined at weekly intervals. The skeletal muscle expression of the ubiquitin proteasome system, myostatin, its receptor (the activin 2B receptor) and its signal, cyclin-dependent kinase inhibitor (CDKI) p21, insulin-like growth factor (IGF)-I and its receptor (IGF-I receptor-alpha), and markers of satellite cell proliferation and differentiation were quantified. PCA rats did not gain body weight and had lower lean body mass, forelimb grip strength, and gastrocnemius muscle weight. The skeletal muscle expression of the mRNA of ubiquitin proteasome components was higher in PCA rats in the first 2 wk followed by a lower expression in the subsequent 2 wk (P<0.01). The mRNA and protein of myostatin, activin 2B receptor, and CDKI p21 were higher, whereas IGF-I and its receptor as well as markers of satellite cell function (proliferating nuclear cell antigen, myoD, myf5, and myogenin) were lower at weeks 3 and 4 following PCA (P < 0.05). We conclude that PCA resulted in uninhibited proteolysis in the initial 2 wk. This was followed by an adaptive response in the later 2 wk consisting of an increased expression of myostatin that may have contributed to reduced muscle protein synthesis, impaired satellite cell function, and lower skeletal muscle mass.

Inhibition of aromatase improves nutritional status following portacaval anastomosis in male rats

BACKGROUND/AIMS

The portacaval anastamosis (PCA) rat is a model of the nutritional and endocrine consequences of liver cirrhosis. We hypothesized that failure to gain body weight in the PCA rat was the consequence of low testosterone levels and will be reversed by 4-hydroxyandrostenedione, a specific aromatase inhibitor.

METHODS

Male Sprague-Dawley rats subjected to an end-to-side PCA or sham surgery were administered either 4-hydroxyandrostenedione or vehicle. Food intake, food efficiency, and body weight were measured, animals sacrificed 3 weeks after surgery, visceral organs harvested and plasma sex steroids measured. Hepatic RNA was extracted and dot blots done to quantify the expression of sex hormone dependent enzymes 16alpha hydroxylase and 15beta hydroxylase.

RESULTS

Growth, food intake, food efficiency and plasma testosterone were lower and plasma estradiol higher in PCA than sham rats. Hepatic expression of testosterone driven 16alpha hydroxylase was lower and estradiol driven 15beta hydroxylase higher in PCA rats. These alterations were reversed by 4-hydroxyandrostenedione.

CONCLUSIONS

These observations demonstrate that use of aromatase inhibitor reverses the nutritional and endocrine abnormalities in the PCA rat and suggest that this approach may be useful in cirrhotic patients.

Skeletal muscle atrophy is associated with an increased expression of myostatin and impaired satellite cell function in the portacaval anastamosis rat

Proliferation and differentiation of satellite cells are critical in the regeneration of atrophied muscle following immobilization and aging. We hypothesized that impaired satellite cell function is responsible for the atrophy of skeletal muscle also seen in cirrhosis. Myostatin and insulin-like growth factor 1 (IGF1) have been identified to be positive and negative regulators, respectively, of satellite cell function. Using a rat model of cirrhosis [portacaval anastamosis (PCA)] and sham-operated controls, we examined the expression of myostatin, its receptor activinR2b, and its downstream messenger cyclin-dependent kinase inhibitor p21 (CDKI p21) as well as IGF1 and its receptor in the gastrocnemius muscle. Expression of PCNA, a marker of proliferation, and myogenic regulatory factors (myoD, myf5, and myogenin), markers of differentiation of satellite cells, were also measured. Real- time PCR for mRNA and Western blot assay for protein quantification were performed. PCA rats had lower body weight and gastrocnemius weight compared with sham animals (P < 0.05). PCNA and myogenic regulatory factors were lower in PCA rats (P < 0.05). Myostatin, activinR2b, and CDKI p21 were higher in the PCA animals (P < 0.05). The expression of IGF1 and its receptor was lower in liver and skeletal muscle of PCA animals (P < 0.05). These data suggest that skeletal muscle atrophy seen in the portacaval shunted rats is a consequence of impaired satellite cell proliferation and differentiation mediated, in part, by higher myostatin and lower IGF1 expression.

Hematotesticular barrier is altered from early stages of liver cirrhosis: Effect of insulin-like growth factor 1

AIM: The pathogenesis of hypogonadism in liver cirrhosis is not well understood. Previous results from our laboratory showed that IGF-1 deficiency might play a pathogenetic role in hypogonadism of cirrhosis. The administration of IGF-1 for a short period of time reverted the testicular atrophy associated with advanced experimental cirrhosis. The aim of this study was to establish the historical progression of the described alterations in the testes, explore testicular morphology, histopathology, cellular proliferation, integrity of testicular barrier and hypophyso-gonadal axis in rats with no ascitic cirrhosis.

METHODS: Male Wistar rats with histologically-proven cirrhosis induced with carbon tetrachloride (CCl₄) for 11 wk, were allocated into two groups (n = 12, each) to receive recombinant IGF-1 (2 μg/100 g.d, sc) for two weeks or vehicle. Healthy rats receiving vehicle were used as control group (n = 12).

RESULTS: Compared to controls, rats with compensated cirrhosis showed a normal testicular size and weight and very few histopathological testicular abnormalities. However, these animals showed a significant diminution of cellular proliferation and a reduction of testicular transferrin expression. In addition, pituitary-gonadal axis was altered, with significant higher levels of FSH (P < 0.001 vs controls) and increased levels of LH in untreated cirrhotic animals. Interestingly, IGF-1 treatment normalized testicular transferrin expression and cellular proliferation and reduced serum levels of LH (P = ns vs controls, and P < 0.01 vs untreated cirrhotic group).

CONCLUSION: The testicular barrier is altered from an early stage of cirrhosis, shown by a reduction of transferrin expression in Sertoli cells, a diminished cellular proliferation and an altered gonadal axis. The treatment with IGF-1 could be also useful in this initial stage of testicular disorder associated with compensated cirrhosis.

Nutrition and survival in patients with liver cirrhosis

Although the effect of malnutrition on survival has been demonstrated by a number of studies, it is not clear whether malnutrition represents an independent risk factor in patients with liver disease. We studied 212 hospitalized patients with liver cirrhosis who were followed clinically for 2 y or until death. Body fat and muscle mass were evaluated by triceps skinfold thickness (TSF) and midarm muscle circumference (MAMC), respectively. Multivariate analysis according to Cox's model assessed the predictive power of nutritional parameters on survival. Thirty-four percent of patients had severe malnutrition as determined by MAMC and/or TSF below the 5th percentile and 20% had moderate malnutrition (MAMC and/or TSF < 10th percentile). Twenty-six percent of patients were overnourished (MAMC and/or TSF > 75th percentile). Severely and moderately malnourished patients had lower survival rates than normal and overnourished patients. When analyzed with Cox's regression analysis, severe depletion of muscle mass and body fat were found to be independent predictors of survival. The inclusion of MAMC and TSF in the Child-Pugh score, the prognostic score used most with liver disease, improved its prognostic accuracy. The prognostic power of MAMC was higher than that of TSF. These data demonstrate that malnutrition is an independent predictor of survival in patients with liver cirrhosis. The inclusion of anthropometric measures in the assessment of these patients might provide better prognostic information.

Insulin-like growth factor-I reverts testicular atrophy in rats with advanced cirrhosis

The pathogenesis of hypogonadism in cirrhosis is not completely understood. The levels of insulin-like growth factor-I (IGF-I), an anabolic factor with trophic actions on testes, are reduced in cirrhosis. This study was undertaken to evaluate whether rats with advanced cirrhosis develop hypogonadism and whether the administration of IGF-I exerts beneficial effects on testicular structure and function. Wistar rats with ascitic cirrhosis induced with CCl(4) were allocated into 2 groups (n = 10, each) to receive recombinant IGF-I (20 microg x kg(-1) x d(-1), subcutaneously) or vehicle for 3 weeks. Healthy rats receiving vehicle were used as the control group (n = 10). At baseline, both cirrhotic groups showed similar deterioration of liver function tests. Compared with controls, nontreated cirrhotic rats showed decreased serum levels of IGF-I (P <.05), reduced testicular size and weight (P <.001), and intense histopathological testicular abnormalities, including reduced tubular diameters (P <.001), loss of the germinal line (P <. 001), and diminutions in cellular proliferation, spermatogenesis (P <.001), and testicular transferrin expression (P <.001). In addition, low serum testosterone (P <.01) and high serum LH (P <.01) were present in untreated cirrhotic animals. Cirrhotic rats that received IGF-I showed full recovery of testicular size and weight and of all histopathological abnormalities (P <.001 to <.01 vs. nontreated cirrhotic rats; P = ns vs. controls). Serum levels of sex hormones tended to normalize. In conclusion, IGF-I deficiency may play a pathogenetic role in hypogonadism of cirrhosis. Low doses of IGF-I for a short period of time revert testicular atrophy and appear to improve hypogonadism in advanced experimental cirrhosis.

Stenosis of a portacaval anastomosis affects circadian locomotor activity in the rat: a multivariable analysis

The study of hepatic encephalopathy is limited by the lack of standardized experimental models to assess behavior. We have shown that rats continuously monitored while running on a wheel show abnormalities of the circadian rhythm of locomotor activity after portacaval anastomosis (PCA), such that entrainment of running activity to the light-dark cycle is severely impaired. To identify factors that affect postoperative circadian behavior, we have performed a multivariable analysis of 69 sham-operated controls and 107 rats after PCA. Our results indicate that shunt stenosis, as determined by the pressure gradient from the splenic pulp to the inferior vena cava, ameliorated the postoperative deterioration of the circadian rhythm. In addition, postoperative behavior was affected by preoperative performance, diet, and gender. Postoperative body weight gain, spleen weight, and liver atrophy did not impact this model. Because shunt stenosis is known to ameliorate hepatic encephalopathy in humans, our findings support the validity of this behavioral end point as a correlate of hepatic encephalopathy. Measurement of the pressure gradient across the anastomosis and achievement of sufficient preoperative entrainment appear critical for the standardization of the model.

Low doses of insulin-like growth factor-I improve nitrogen retention and food efficiency in rats with early cirrhosis

BACKGROUND/AIMS

In order to ascertain whether malnutrition is an early-onset feature of liver cirrhosis and whether the anabolic hormone insulin-like growth factor I (IGF-I) could be useful in the treatment of this complication, we analyzed the nutritional alterations present in rats with early-stage liver cirrhosis and the effects of IGF-I on nutritional parameters in these animals.

METHODS

After a 24 h fast, a 15N-enriched diet was administered for 5 days to normal control rats and to cirrhotic rats receiving subcutaneous injections of vehicle (Group 1) or IGF-I, 2 micrograms.100 g bw-1.day-1, (Group 2) during the 5 experimental days. 15N, a stable N isotope, was measured in biological samples by mass spectrometry.

RESULTS

Compared with control rats, Group 1 animals showed significant reductions in N intake and food efficiency (p < 0.05, both). In addition, the weight of the gastrocnemius muscle, its total N content and the dietary N content of this muscle were significantly lower in Group 1 than in control animals (p < 0.05, all). In rats from Group 2, mean values of N intake, food efficiency, gastrocnemius N content and the amount of dietary N incorporated into this muscle were similar to those in control rats, and (with the exception of gastrocnemius N total content) significantly higher than those in non-treated cirrhotic rats (p < 0.05, all).

CONCLUSIONS

A variety of nutritional disturbances were detected in rats from the early stages of liver cirrhosis. Low doses of IGF-I were found to reverse most of these changes. These results stimulate further studies to determine whether IGF-I might be useful in the correction of the malnutrition present in patients with liver cirrhosis.