Differences in pituitary cell number but not cell type between genetically lean and fat Coopworth sheep

Anatomy and histology of the Göttingen minipig adenohypophysis with special emphasis on the polypeptide hormones: GH, PRL, and ACTH

The pituitary is involved in the regulation of endocrine homeostasis. Therefore, animal models of pituitary disease based on a thorough knowledge of pituitary anatomy are of great importance. Accordingly, we aimed to perform a qualitative and quantitative description of polypeptide hormone secreting cellular components of the Göttingen minipig adenohypophysis using immunohistochemistry and stereology. Estimates of the total number of cells immune-stained for adrenocorticotrophic hormone (ACTH), prolactin (PRL), and growth hormone (GH) were obtained with the optical fractionator technique using Stereo Investigator software. Moreover, 3D reconstructions of cell distribution were made. We estimated that the normal minipig adenohypophysis contains, on average, 5.6 million GH, 3.5 million PRL, and 2.4 million ACTH producing cells. The ACTH producing cells were widely distributed, while the PRL and GH producing cells were located in clusters in the central and lateral regions of the adenohypophysis. The morphology of the hormone producing cells also differs. We visualized a clear difference in the numerical density of hormone producing cells throughout the adenohypophysis. The relative proportions of the cells analyzed in our experiment are comparable to those observed in humans, primates, and rodents; however, the distribution of cells differs among species. The distribution of GH cells in the minipig is similar to that in humans, while the PRL and ACTH cell distributions differ. The volume of the pituitary is slightly smaller than that of humans. These data provide a framework for future large animal experimentation on pituitary function in health and disease.

Variation in the FABP4 gene affects carcass and growth traits in sheep

Fatty acid-binding protein 4 (FABP4) participates in fatty-acid transportation and variation in the gene has been reported to affect fat deposition in mammals. To assess the effects of variation in FABP4 on carcass and growth traits in sheep, two regions of the gene were investigated in 749 New Zealand Romney lambs. Five variants (A₁ - E₁) were found in region-1 (exon 2 - intron 2) and three variants (A₂ - C₂) were found in region-2 (exon 3 - intron 3). A₁ was associated with a decrease in leg meat yield, loin meat yield and total meat yield, whereas A₂ was associated with a decrease in weaning-weight and pre-weaning growth-rate. Haplotype A₁-A₂ was found to be associated with a decrease in birth-weight, pre-weaning growth-rate, hot carcass weight, loin meat yield, shoulder meat yield and total meat yield, while haplotype A₁-B₂ was associated with increased fat depth at the 12th rib (V-GR). Taken together, this supports the contention that variation in FABP4 affects growth and meat production in sheep.

Adipose and skeletal muscle thermogenesis: studies from large animals

The balance between energy intake and energy expenditure establishes and preserves a 'set-point' body weight. The latter is comprised of three major components including metabolic rate, physical activity and thermogenesis. Thermogenesis is defined as the cellular dissipation of energy via heat production. This process has been extensively characterised in brown adipose tissue (BAT), wherein uncoupling protein 1 (UCP1) creates a proton leak across the inner mitochondrial membrane, diverting protons away from ATP synthesis and resulting in heat dissipation. In beige adipocytes and skeletal muscle, thermogenesis can occur independent of UCP1. Beige adipocytes have been shown to produce heat via UCP1 as well as via both futile creatine and calcium cycling pathways. On the other hand, the UCP1 homologue UCP3 is abundant in skeletal muscle and post-prandial thermogenesis has been associated with UCP3 and the futile calcium cycling. This review will focus on the differential contributions of adipose tissue and skeletal muscle in determining total thermogenic output and energy expenditure in large mammals. Sheep and pigs do not have a circumscribed brown fat depot but rather possess white fat depots that contain brown and beige adipocytes interspersed amongst white adipose tissue. This is representative of humans, where brown, beige and white adipocytes have been identified in the neck and supraclavicular regions. This review will describe the mechanisms of thermogenesis in pigs and sheep and the relative roles of skeletal muscle and adipose tissue thermogenesis in controlling body weight in larger mammals.

Differences in mitochondrial DNA inheritance and function align with body conformation in genetically lean and fat sheep

Body weight and adiposity are determined by the balance between energy intake, energy expenditure, and nutrient deposition. We have identified differences in appetite-regulating peptides in sheep selectively bred to be either lean or fat, wherein gene expression for orexin and melanin-concentrating hormone are elevated in the lean group. Despite this, the underlying mechanisms leading to differences in body composition in the lean and fat lines remains unknown. We measured postprandial temperature in adipose tissue and muscle to ascertain whether a difference in thermogenesis is associated with the difference in body composition in genetically lean (n = 8) and fat (n = 12) ewes. Body weight was higher (P < 0.01) but percent fat mass was lower (P < 0.001) in the lean group. The percent lean mass was similar in lean and fat groups. Animals received intracerebroventricular cannulae and temperature probes implanted into the retroperitoneal fat and the hind-limb skeletal muscle (vastus lateralis). Animals were meal fed (1100-1600 h) to entrain postprandial thermogenesis. Food intake was similar between lean and fat animals. Postprandial thermogenesis was greater (P < 0.05) in the retroperitoneal adipose tissue of lean animals but not in skeletal muscle. Intracerebroventricular infusion of leptin reduced (P< 0.05) food intake by an equal extent in both groups. Postprandial expression of UCP1 mRNA was greater (P < 0.05) in retroperitoneal fat of lean animals, with similar UCP3 expression in skeletal muscle. Mitochondrial genome sequencing indicated haplotypic clustering in lean and fat animals within both the encoding and nonencoding regions. This demonstrates that differences in body composition may be underpinned by differences in thermogenesis, specifically within adipose tissue. Furthermore, thermogenic differences may be associated with specific mitochondrial DNA haplotypes, suggesting a strong genetic component inherited through the maternal lineage.

Interface between metabolic balance and reproduction in ruminants: focus on the hypothalamus and pituitary

This article is part of a Special Issue "Energy Balance". The interface between metabolic regulators and the reproductive system is reviewed with special reference to the sheep. Even though sheep are ruminants with particular metabolic characteristics, there is a broad consensus across species in the way that the reproductive system is influenced by metabolic state. An update on the neuroendocrinology of reproduction indicates the need to account for the way that kisspeptin provides major drive to gonadotropin releasing hormone (GnRH) neurons and also mediates the feedback effects of gonadal steroids. The way that kisspeptin function is influenced by appetite regulating peptides (ARP) is considered. Another newly recognised factor is gonadotropin inhibitory hormone (GnIH), which has a dual function in that it suppresses reproductive function whilst also acting as an orexigen. Our understanding of the regulation of food intake and energy expenditure has expanded exponentially in the last 3 decades and historical perspective is provided. The function of the regulatory factors and the hypothalamic cellular systems involved is reviewed with special reference to the sheep. Less is known of these systems in the cow, especially the dairy cow, in which a major fertility issue has emerged in parallel with selection for increased milk production. Other endocrine systems--the hypothalamo-pituitary-adrenal axis, the growth hormone (GH) axis and the thyroid hormones--are influenced by metabolic state and are relevant to the interface between metabolic function and reproduction. Special consideration is given to issues such as season and lactation, where the relationship between metabolic hormones and reproductive function is altered.

Allelic variation in ovine fatty acid-binding protein (FABP4) gene

The fatty acid-binding protein 4 (FABP4) plays a role in lipid metabolism and has been implicated in intra-cellular lipid transport. While FABP4 variation has been reported in some species, variation in the coding sequence has not been reported in sheep. In this study two regions of ovine FABP4 were analysed using PCR-SSCP and sequencing. Five different PCR-SSCP patterns, representing five specific sequences (A ( 1 )-E ( 1 )) were detected in region 1 (exon 2-intron 2) with sequence analysis revealing three nucleotide substitutions and one deletion in the intron. In region 2 (exon 3-intron 3), four different PCR-SSCP patterns (A ( 2 )-D ( 2 )) were observed and four nucleotide substitutions were revealed. In total, fourteen haplotypes through both regions were defined. There was a difference (P < 0.001) in allele frequencies between two selection lines of Coopworth sheep that have been bred over many generations to be lean or fat. In region 1, A ( 1 ) and B ( 1 ) were most common (at a frequency of 50 and 30 % respectively) in the fat line, whereas these two variants were absent or rare in the lean line in which C ( 1 ) predominated (89 %). In region 2, C ( 2 ) was the most common variant (59 %) in the lean line but was absent in the fat line, whereas B ( 2 ) was predominant (83 %) in the fat line but was rare (3 %) in the lean line. These results indicate that ovine FABP4 is polymorphic and suggest further analysis is required to see if the variation detected affects fat deposition in sheep.

Growth hormone and ghrelin receptor genes are differentially expressed between genetically lean and fat selection lines of sheep

The objective of this study was to determine whether differences in mRNA levels of key pituitary genes that regulate GH production, pituitary development, and growth were present and/or associated with divergent body composition phenotypes observed between sheep from genetically divergent lean and fat selection lines. Real-time PCR transcription profiles for pituitary specific transcription factor 1, prophet of pit1, GH, GH receptor, GH secretagogue receptor, GHRH receptor, leptin receptor, and somatostatin receptors 1 and 2 were determined in pituitary tissue. There was a difference in the amount of both GH (P < 0.001) and GH secretagogue receptor (P < 0.001) mRNA between the selection lines (5 females and 5 males per line; 20 wk of age); the lean line had greater abundance than the fat line, irrespective of which endogenous control gene was used. The results obtained for GHRH receptor were equivocal but suggestive; there were greater GHRH receptor mRNA levels (P < 0.001) in the lean line using beta-2-microglobulin as the endogenous control but not when hypoxanthine phosphoribosyltransferase and glyceraldehyde-3-phosphate dehydrogenase were used. No difference in pituitary specific transcription factor 1, prophet of pit1, GH receptor, leptin receptor, or somatostatin receptors 1 and 2 mRNA concentration was observed between the lines. The greater abundance of GH mRNA in the pituitary somatotropes from genetically lean animals appears to be associated with increased levels of GH secretagogue receptor mRNA and possibly GHRH receptor mRNA. This suggests that the difference in GH secretion between the lines may be due to differences in the afferent signals, such as ghrelin and/or GHRH, arising from the hypothalamus, or as a result of differential pituitary sensitivity to these hormones.