Comparison of DNA synthesis in white and brown adipose tissue in rats with ventromedial hypothalamic lesions

Carbachol induces hepatocyte proliferation, but only in the presence of hepatic nonparenchymal cells

Vagal hyperactivity correlates with enhanced DNA synthesis and cell proliferation in the peripheral tissues of ventromedial hypothalamic (VMH)-lesioned rats. The infusion of an ACh receptor agonist, carbachol (Cch), induces rat duodenal and pancreatic cell proliferation to a degree comparable to the VMH lesions. Whereas the VMH lesions also induce the proliferation of hepatic cells, it is unclear whether Cch can also do this. Here we attempted to clarify the mechanism of hepatic cell proliferation induction by cholinergic stimulation. First, hepatic cell proliferation was examined in rats previously vagotomized and intraperitoneally administered with Cch via an osmotic minipump. Second, the sera from the Cch-infused rats were examined for a proliferative effect on isolated hepatic cells. And last, the effect of the presence of hepatic nonparenchymal cells (NPCs) on the proliferation of the cultured hepatocytes treated with Cch was investigated. Immunohistochemistry for proliferating cell nuclear antigen (PCNA) showed that the 3-day Cch infusion significantly increased the number of PCNA-immunoreactive cells in the liver. Moreover, the sera from the Cch-infused rats increased the number of PCNA-immunoreactive hepatocytes in culture. However, Cch alone did not induce proliferation in monocultured hepatocytes. When compared with the monoculture of hepatocytes, the coculture of those with hepatic NPCs resulted in enhanced PCNA immunoreactivity after a 4-day treatment with 3 mM Cch. These findings suggest that ACh induces hepatocyte proliferation, which is mediated by unidentified humoral factor(s) possibly secreted from hepatic NPCs, and that it also participates in liver hypertrophy in the VMH-lesioned animals.

Continuous carbachol infusion promotes peripheral cell proliferation and mimics vagus hyperactivity in a rat model of hypothalamic obesity

Lesions of the ventromedial hypothalamus (VMH) result in obesity and enhanced cellular proliferation in various organs, including the pancreas, gastrointestinal tract, and liver. Previous studies have suggested that vagal hyperactivity, rather than overeating, induces the peripheral cell proliferation in VMH-lesioned rats. The goal of the present study was to investigate the mechanism of peripheral cell proliferation in VMH-lesion-induced obesity by infusing rats with the acetylcholine agonist, carbachol, and then measuring cellular proliferation in the pancreas and duodenum using immunohistochemistry. The ventromedial hypothalamus was bilaterally lesioned in five rats. In other rats, the bilateral vagus nerves were ligated (vagotomized), and saline or carbachol was continuously administered by an osmotic minipump (n = 5 in each group). Three days later, rats were killed, and cell proliferation was assessed in the pancreas and the duodenum using immunohistochemistry for proliferating cell nuclear antigen (PCNA). Additionally, cellular proliferation in the duodenum was more precisely examined by assessing incorporation of 5-bromo-2'-deoxyuridine (BrdU). Cellular proliferation was higher in rats that received carbachol infusions and in rats with VMH-lesions when compared with control rats (P < 0.05, respectively). The pancreatic PCNA-expressing cells were predominantly identified as the B-cells of the islets of Langerhans. These data demonstrate that carbachol infusion can induce pancreatic and duodenal cell proliferation to a degree that was comparable to that in vagal hyperactivity induced by VMH lesions.

cDNA cloning and tissue-specific gene expression of ovine leptin, NPY-Y1 receptor, and NPY-Y2 receptor

The physiological regulation of food intake is a critical factor in both the rate at which an animal grows and its reproductive activity. Recently, progress has been made in elucidating a complex system in which insulin, leptin, and neuropeptide Y function to monitor an animal's energy balance and regulate feed intake and fertility. RNA was extracted from ovine hypothalamic, anterior pituitary, pancreas, and adipose tissue. Using the reverse transcription-polymerase chain reaction. cDNAs were cloned and sequenced for leptin (350 base pairs [bp], GenBank accession number U62123 and 441 bp, GenBank accession number U84247), NPY-Y1 receptor (350 bp, GenBank accession no. U62122) and NPY-Y2 receptor (440 bp, GenBank accession no. U83458). Probes generated from these clones were used to detect mRNA expression within tissues thought to be involved in the coregulation of feed intake and reproduction. Leptin was found to be expressed in sheep adipose tissue. The ovine NPY-Y1 receptor mRNA was detected within the arcuate nucleus and paraventricular nucleus of the hypothalamus, the dentate gyrus of the hippocampus and in pancreatic, anterior pituitary, and adipose tissues. Expression of ovine NPY-Y2 receptor mRNA was detected in the hippocampus and within pancreatic tissue. These observations provide evidence of potential mechanisms that exist for mediating communication between peripheral and central tissues within the insulin-leptin-NPY pathway.

Leptin receptor mRNA is expressed in ewe anterior pituitary and adipose tissues and is differentially expressed in hypothalamic regions of well-fed and feed-restricted ewes

Infertility associated with suboptimal nutrition is a major concern among livestock producers. Recently, much effort has been put into understanding the role of the protein leptin in regulating feed intake and reproduction. Leptin, produced by adipocytes, has receptors in the hypothalamus, but more precise locations of leptin receptor-expressing cell bodies have not been reported in a livestock species. The leptin receptor transcript has several splice variants in the mouse and human, but only the "long-form" product (OBRL) is capable of signal transduction. A partial ovine long-form leptin receptor cDNA was cloned and used to evaluate OBRL mRNA expression within hypothalamic, anterior pituitary, and adipose tissues of ovariectomized adult ewes. Expression was detected in reverse transcription-polymerase chain reaction products of all tissues examined. OBRL mRNA was detected by in situ hybridization in the ventromedial and arcuate nuclei of the hypothalamus. In ewes that had been feed restricted for 3 wk before tissue collection, the expression of OBRL mRNA in these areas was greater (P < 0.05) than that found in well-fed ewes. These findings provide evidence that the full-length leptin receptor is expressed in hypothalamic, anterior pituitary, and adipose tissue (the latter proffering an autoregulatory mechanisms for leptin) and that within the hypothalamus, this receptor form is differentially expressed in well-fed vs. feed-restricted animals.

Lateral hypothalamic lesions facilitate hepatic regeneration after partial hepatectomy in rats

It has been reported that ventromedial hypothalamic lesions facilitate hepatic regeneration through the hepatic vagal nerve after partial hepatectomy. However, whether the lateral area of the hypothalamus is involved in liver regeneration after partial hepatectomy is unknown. To determine the role of the lateral hypothalamic area in this phenomenon, we studied hepatic DNA synthesis during liver regeneration after partial hepatectomy with bilateral lesions of the area. Lesioning of the lateral hypothalamus accelerated the increase in hepatic DNA synthesis and raised the peak level of [methyl-3H]thymidine incorporation after partial hepatectomy. These effects of hypothalamic lesioning were inhibited by combined hepatic vagotomy and sympathectomy. Our results demonstrate that lesioning of the lateral hypothalamus promotes hepatic regeneration through the autonomic nervous system after partial hepatectomy and suggest that the lateral hypothalamic area is involved in liver regeneration through neural mediation.

Facilitation of liver regeneration after partial hepatectomy by ventromedial hypothalamic lesions in rats

Whether or not the hypothalamus is involved in initiating hepatic DNA synthesis after partial hepatectomy is unclear. To determine the role of the ventromedial hypothalamic nuclei in liver regeneration after partial hepatectomy, we studied hepatic DNA synthesis during liver regeneration in rats with bilateral lesions of these nuclei. Lesions of the ventromedial hypothalamus accelerated the increase in hepatic DNA synthesis and raised the peak level of thymidine incorporation after partial hepatectomy. These effects of hypothalamic lesions were completely inhibited by hepatic vagotomy. Thus, lesions of the ventromedial hypothalamus appear to promote hepatic regeneration by increasing vagal stimulation of the liver.