Plasma oxytocin, prolactin, insulin and LH after 24 h of fasting and after refeeding in lactating sows

Impact of arginine supplementation on serum prolactin and mRNA abundance of amino acid transporter genes in mammary tissue of lactating sows

This study was conducted to test the hypothesis that supplemental dietary Arg to late-pregnant and lactating sows increases serum prolactin concentrations and mRNA abundance of SLC7A1, SLC7A2, and SLC6A14 in mammary parenchymal tissue. From day 108 of gestation and until day 21 of lactation, sows were fed a diet either supplemented with 0.10 g of l-Arg/kg body weight (BW) per day (n = 10, ARG) or 0.34 g of l-Glu/kg BW per day (n = 10, control). Litters were standardized to 10 piglets on day 1 of lactation and piglets were weighed on days 1, 7, 14, and 21 of lactation. Sow BW was recorded on day 108 of gestation and days 1, 10, and 21 of lactation. Lactation sow feed intake was recorded daily. Mammary parenchymal tissue was biopsied on day 5 of lactation to measure mRNA abundance SLC7A1, SLC7A2, and SLC6A14. On days 4 and 18 of lactation, blood samples were collected from sows at 2, 4, and 6 hr postfeeding to measure serum prolactin concentrations. Milk samples were collected on days 4, 10, and 18 of lactation to measure fat, lactose, urea N, and true protein concentrations. Sow BW, backfat, and feed intake over all sampling days did not differ between treatments. Piglet BW on d 1 tended to be greater for the ARG treatment than the control treatment (P = 0.12). Sow milk yield and composition (fat, protein, lactose, and urea N) and mammary mRNA abundance of candidate genes did not differ between the ARG and the control group. Compared to controls, serum prolactin concentrations tended to be greater (P = 0.08) in ARG sows on day 4 of lactation, and did not differ on day 18. Current findings show a potential beneficial effect of dietary supplementation with Arg to late-pregnant multiparous sows on BW of their piglets on day 1. Dietary Arg supplementation at a rate of 0.10 g/kg BW during late pregnancy and lactation tended to increase serum prolactin concentrations with no increase in mammary transcript abundance of SLC7A1, SLC7A2, and SLC6A14 in early lactation.

Altering prolactin concentrations in sows

Prolactin has a multiplicity of actions, but it is of particular importance in gestating and lactating animals. In sows, it is involved in the control of mammary development and also holds essential roles in the lactogenic and galactopoietic processes. Furthermore, low circulating concentrations of prolactin are associated with the agalactia syndrome. The crucial role of prolactin makes it important to understand the various factors that can alter its secretion. Regulation of prolactin secretion is largely under the negative control of dopamine, and dopamine agonists consistently decrease prolactin concentrations in sows. On the other hand, injections of dopamine antagonists can enhance circulating prolactin concentrations. Besides pharmacologic agents, many other factors can also alter prolactin concentrations in sows. The use of Chinese-derived breeds, for instance, leads to increased prolactin concentrations in lactating sows compared with standard European white breeds. Numerous husbandry and feeding practices also have a potential impact on prolactin concentrations in sows. Factors, such as provision of nest-building material prepartum, housing at farrowing, high ambient temperature, stress, transient weaning, exogenous thyrotropin-releasing factor, exogenous growth hormone-releasing factor, nursing frequency, prolonged photoperiod, fasting, increased protein and/or energy intake, altered energy sources, feeding high-fiber diets, sorghum ergot or plant extracts, were all studied with respect to their prolactinemic properties. Although some of these practices do indeed affect circulating prolactin concentrations, none leads to changes as drastic as those brought about by dopamine agonists or antagonists. It appears that the numerous factors regulating prolactin concentrations in sows are still not fully elucidated, and that studies to develop novel applicable ways of increasing prolactin concentrations in sows are warranted.

Expression and regulation of α-transducin in the pig gastrointestinal tract

Taste signalling molecules are found in the gastrointestinal (GI) tract suggesting that they participate to chemosensing. We tested whether fasting and refeeding affect the expression of the taste signalling molecule, α-transducin (G_αtran), throughout the pig GI tract and the peptide content of G_αtran cells. The highest density of G_αtran-immunoreactive (IR) cells was in the pylorus, followed by the cardiac mucosa, duodenum, rectum, descending colon, jejunum, caecum, ascending colon and ileum. Most G_αtran-IR cells contained chromogranin A. In the stomach, many G_αtran-IR cells contained ghrelin, whereas in the upper small intestine many were gastrin/cholecystokinin-IR and a few somatostatin-IR. G_αtran-IR and G_αgust-IR colocalized in some cells. Fasting (24 h) resulted in a significant decrease in G_αtran-IR cells in the cardiac mucosa (29.3 ± 0.8 versus 64.8 ± 1.3, P < 0.05), pylorus (98.8 ± 1.7 versus 190.8 ± 1.9, P < 0.0 l), caecum (8 ± 0.01 versus 15.5 ± 0.5, P < 0.01), descending colon (17.8 ± 0.3 versus 23 ± 0.6, P < 0.05) and rectum (15.3 ± 0.3 versus 27.5 ± 0.7, P < 0.05). Refeeding restored the control level of G_αtran-IR cells in the cardiac mucosa. In contrast, in the duodenum and jejunum, G_αtran-IR cells were significantly reduced after refeeding, whereas G_αtran-IR cells density in the ileum was not changed by fasting/refeeding. These findings provide further support to the concept that taste receptors contribute to luminal chemosensing in the GI tract and suggest they are involved in modulation of food intake and GI function induced by feeding and fasting.

Fasting stimulates tuberoinfundibular dopaminergic neuronal activity and inhibits prolactin secretion in oestrogen-primed ovariectomized rats: involvement of orexin A and neuropeptide Y

Fasting up-regulates central orexigenic systems including orexin A and neuropeptide Y (NPY) and it also inhibits the secretion of prolactin. We hypothesized that fasting may act through orexin A and NPY to influence tuberoinfundibular dopaminergic (TIDA) neurones, the major regulator of prolactin secretion. The effects of orexin A and NPY on TIDA neuronal activity and prolactin secretion were determined in oestrogen-primed ovariectomized rats, and the effects of fasting and the involvement of orexin A and NPY were tested. Orexin A, NPY and its analogs were administered through preimplanted intracerebroventricular (i.c.v.) cannulae. TIDA neuronal activity was determined by measuring concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) or 3,4-dihydroxyphenylalanine in the median eminence. i.c.v. injection of NPY (10 microg) or orexin A (1 microg) concomitantly increased median eminence DOPAC and decreased serum prolactin concentrations. The effect of NPY was mimicked by a Y1 receptor agonist at lower doses (0.1 and 1 microg) and no additive effect was observed when orexin A and the Y1 agaonist were coadministered. Moreover, a Y1 receptor antagonist, BIBP, not only blocked the effect of Y1 agaonist, but also that of orexin A. Treatment with BIBP alone decreased median eminence DOPAC and increased serum prolactin concentrations, indicating that endogenous NPY may play a role. Moreover, fasting for 48 h significantly increased TIDA neuronal activity, both in the morning and afternoon, and the effect was reversed by treatment with either BIBP or an antibody against orexin A. The findings support our hypothesis that fasting stimulates TIDA neuronal activity and inhibits prolactin secretion through up-regulated central orexin A and NPY systems.

A sexual arousability model involving steroid effects at the plasma membrane

This review will discuss the status of research related to sexual arousability. It will also present a model for sexual arousability based on current knowledge of steroids effects at the membranes of cells. Steroids have multiple rapid actions that are suggested to result from actions at membrane-associated receptors. When stimulated by steroids these receptors alter G-protein coupling in a manner unique to this complex. Initial stimulation of the receptors by steroids alters the coupling pattern of G-proteins and of other binding sites associated with the complex. This change in G-protein coupling is a stable alteration and thus may serve as a long-term change in the system, which is a requirement of sexual arousability. Stimulation of this receptor system by a surge of oxytocin at ejaculation or orgasm then decouples the G-protein and reduces arousability. Sex hormone binding globulin may be an important ligand at this complex. This model suggests completely new relationships among steroids and their receptors that may complement or diverge from actions at known intracellular receptors.

Effects of post-ovulatory food deprivation on the hormonal profiles, activity of the oviduct and ova transport in sows

The objective of the present study was to investigate the effect of post-ovulatory food deprivation on the hormonal profiles and consequently on the activity of the oviduct and ova transport in sows. Sows were randomly allocated to the control (C-group, n=6) or fasted (F-group, n=5) group. The F-group sows were fasted for four meals starting with the morning meal after detection of ovulation in the second oestrus after weaning. Ovulation was checked by transrectal ultrasonography. Blood was collected for the analyses of progesterone, oestradiol-17beta, prostaglandin F(2 approximately ) metabolite, insulin, free fatty acids and triglycerides. Oviductal isthmic motility was monitored on Polyview before and after ovulation until the time of slaughter. After slaughter, the isthmus opposite the side with transducer was divided into three equal segments and flushed separately and a third of the uterine horn part from the utero-tubal-junction (UTJ) was also flushed. A high proportion of ova in the F-group was found in the first and second parts of the isthmus. In the C-group, a high proportion of ova was found in the third part of the isthmus and the uterus. The mean isthmic pressure in the C-group decreased significantly (P<0.05) during the period immediately after ovulation while in the F-group mean pressure remained unchanged. The frequency of phasic pressure fluctuations were significantly (P<0.05) higher in the F- than in the C-group 13 to 24 h after ovulation. No significant differences in progesterone concentrations were seen between the two groups of sows. Prostaglandin metabolite levels were significantly (P<0.05) higher in the F-group than in the C-group. Oestradiol-17beta levels significantly (p<0.05) decreased earlier in the F- than in the C-group. Serum insulin levels were significantly (p=0.05) lower in the F- than in the C-group while free fatty acids were significantly (p<0.01) higher in the F- than in the C-group. There were no significant differences in the serum levels of triglycerides between the F- and the C-group. Therefore, it can be concluded in the present study that food deprivation is associated with changes in the hormonal profiles, activity of the oviduct and a delay of ova transport in sows.

Effects of post-ovulatory food deprivation on oviductal sperm concentration, embryo development and hormonal profiles in the pig

Nutrition is one of the multiple factors that modulate reproduction in animals. The effect of 48 h food deprivation on reproductive and metabolic hormonal changes in relation to cleavage rates was studied. Insemination of 15 sows was performed 20-10 h prior to expected ovulation and ova were recovered at slaughter 65-91 h post ovulation. Blood samples were collected every second hour, beginning from the time of insemination until slaughter, for measurements of progesterone, cortisol, the prostaglandin F2alpha metabolite (15-keto-13,14-dihydro-PGF2alpha) and insulin levels. The embryos from the food-deprived sows (D-group) had fewer accessory spermatozoa in their zona pellucida (ZP) compared with the control sows (C-group). A lower cleavage rate of the embryos in the D-group compared with the C-group was detected. Plasma progesterone, cortisol and prostaglandin F2alpha metabolite levels were significantly higher in the D-group compared with the C-group. Food deprivation is associated with changes in reproductive and metabolic hormones that might lead to changes in the oviductal environment, culminating in a lower cleavage rate of the embryos and presence of fewer viable spermatozoa in the reservoir.

A possible involvement of VIP in feeding-induced secretion of ACTH and corticosterone in the rat

For decades it has been known that brain/gut peptides are released during the ingestion of a meal. Although a multitude of actions have been attributed to these peptides acting in the brain, including the release or inhibition of a variety of pituitary hormones, the actual physiological roles of these substances in the brain have not been confirmed. For the first time, we have demonstrated that feeding-induced hypothalamic-pituitary-adrenal (HPA) secretion may involve the brain/gut peptide, vasoactive intestinal peptide (VIP), acting in the paraventricular nucleus (PVN) of the hypothalamus. The effects of 24 h fasting and refeeding on the release of plasma ACTH and CORT secretion in male rats were investigated. Blood samples were collected 5 min prior to PVN administration of saline or VIP antagonist, [Lsy, Pro, Arg, Tyr]-VIP and 30 min after refeeding. Plasma ACTH and CORT concentrations were significantly increased by 43 and 485%, respectively, by 30 min ingestion of food. Pretreatment with the VIP antagonist (0.75 and 1.5 nmol/rat) significantly reduced the food-induced ACTH response by 69 and 76% and the CORT response by 58 and 65%, respectively. There were no significant differences in food-intake among groups. These results suggest that one potential role of hypothalamic VIP may involve activation of hypothalamic-releasing factors to regulate ACTH and CORT levels during or after a meal.

Role of vagal nerve activity during suckling. Effects on plasma levels of oxytocin, prolactin, VIP, somatostatin, insulin, glucagon, glucose and of milk secretion in lactating rats

The aim of this study was to investigate the role of vagal nerve activity for the release of oxytocin, prolactin and gastrointestinal (GI) hormones during suckling as well as for the secretion of milk in lactating rats. We have therefore performed experiments on vagotomized lactating rats. The animals were decapitated and trunk blood was collected from nonsuckling rats and from suckling rats in connection with milk ejection. Oxytocin, prolactin, vasoactive intestinal polypeptide (VIP), somatostatin, insulin, glucagon and glucose levels in plasma were measured by RIA-technique. In addition, maternal weight as well as the weight of the litters were recorded 7 d after vagotomy. As expected, oxytocin and prolactin levels rose in response to suckling in sham-operated controls. In vagotomized animals the suckling-induced increase of oxytocin was blocked and prolactin levels were significantly decreased. VIP levels in plasma increased following suckling in sham-operated animals and failed to respond after vagotomy. In contrast, somatostatin levels that rose significantly in sham-operated rats were even more significantly raised in vagotomized animals. In addition, insulin but not glucagon levels were increased by suckling. The insulin response, however, persisted after vagotomy. Interestingly, suckling was followed by a lowering of blood-glucose levels in vagotomized, but not in sham-operated animals. The vagotomized rats ate as much and increased in weight as sham-operated rats during the 7 d of vagotomy. The litters of vagotomized rats, however, gained significantly less weight in comparison with control litters. In conclusion, this study shows that vagal nerve activity is of importance for the release of oxytocin, prolactin, vasoactive intestinal polypeptide and somatostatin during suckling.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of efferent and afferent vagal nerve activity during reproduction: integrating function of oxytocin on metabolism and behaviour

The vagal nerves convey information between the brain and the gastrointestinal tract in both afferent and efferent direction. The efferent vagal nerves regulate gastrointestinal secretory and motor function and also the activity in the endocrine system of the gut. Gastrointestinal function and anabolic metabolism is optimized during gestation and lactation as a means of saving energy for this calorie-demanding process. This enhanced activity seems to involve central oxytocinergic transmission which increases efferent vagal nerve activity as reflected by altered levels of gastrointestinal hormones in plasma. In parallel a behaviour pattern characterized by sedation is induced. In addition, vagal afferents transfer information from the gut to the brain, e.g. as to the presence or absence of calories in the gastrointestinal tract. It is well known that satiety and sedation following a meal is in part caused by an activation of vagal afferents in response to food intake. Cholecystokinin released from the intestine is one of the factors that triggers the afferent vagal nerve activity. Also reproductive "interactive behaviours" such as milk ejection and maternal behaviour can be induced by CCK via afferent activation of vagal nerves. In contrast, when no food reaches the gut, milk production and ejection is blocked. Parts of these effects are vagally mediated, since they can be observed in vagotomized rats receiving full amounts of calories.

Patterns of release of oxytocin, prolactin, insulin and LH in lactating sows, studied using continuous blood collection technique

To describe the patterns of release of oxytocin, prolactin, insulin and LH in relation to suckling and to investigate relationships between them, blood was collected continuously from four sows at a rate of 1 ml per min for 12 h (0900-2100 h) on day 10 (D10) and day 20 (D20) of lactation. The 12-h period was divided into four smaller periods: P1 (0900-1200 h), P2 (1200-1500 h), P3 (1500-1800 h) and P4 (1800-2100 h). The number of nursings occurring during a 12-h period tended to decrease between D10 (17.3 +/- 0.3) and D20 (16.0 +/- 0.3). About 40-50% of all sucklings induced a significant rise in plasma oxytocin, while prolactin gradually increased following each suckling. Decrease in the levels of oxytocin (14.1 +/- 0.4 vs 7.1 +/- 0.4 pmol/l, P < 0.001), prolactin (12.9 +/- 0.3 vs 7.9 +/- 0.1 micrograms/l, P < 0.001) and insulin (24.8 +/- 1.7 vs 14.4 +/- 1.7 mU/l, P < 0.001) were observed between D10 and D20. Average and basal levels of LH and the number of LH pulses increased (P < 0.01) between D10 and D20. A negative correlation between number of sucklings and number of LH pulses was demonstrated on D20 (r = -0.59, P = 0.07). There was a positive correlation between levels of LH and oxytocin on D10 (r = 0.54, P = 0.001) and between prolactin and insulin levels on D20 (r = 0.34, P = 0.05).