Pituitary and ovarian response to transient doe-litter separation in nursing rabbits

The effects of a transient doe-litter separation on plasma prolactin, FSH and oestradiol concentrations, as well as the effect on LH response to exogenous GnRH administered at the time of artificial insemination, were determined in nursing rabbits. The effects on fertility, and litter size after parturition, as well as litter survival after doe-litter separation, were also studied. Control does (n = 12) had free access to nursing, whereas biostimulated does (n = 12) were separated from their litters for 48 h before artificial insemination. Plasma prolactin concentrations were decreased 24 h after the doe-litter separation (P < 0.05). The response of prolactin to suckling reached 10 times the basal values measured on day 10 after parturition (P < 0.0001). Increased oestradiol concentrations were found during the 48 h after the doe-litter separation: at 0 h, before artificial insemination (P< 0. 0001), 1.0-2.0 h after artificial insemination (P < 0.001), at 2.5 h (P < 0.05), 3.0 h (P < 0.01), and at 3.5 h (P < 0.05) after artificial insemination. Exogenous GnRH administered at the time of artificial insemination caused a greater LH response in does previously separated from their litters during 48 h (P < 0.01). The transient doe-litter separation did not affect plasma FSH concentrations, fertility, litter size or litter survival. These results suggest that a transient separation of nursing does from their litters before artificial insemination results in a decrease in plasma prolactin concentrations that could promote growth of follicular waves, and high steroidogenesis activity, leading to increased oestradiol concentrations and inducing higher sensitivity of the pituitary gland to exogenous GnRH. These findings associated to the absence of suckling episodes would lead to higher LH response and, therefore, exert a major effect on fertility.     

Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17β and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p<0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17β concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p<0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17β concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p<0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-l7β concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.     

Dietary restriction amplifies the metabolic disturbances of very-low-density lipoproteins in cholesterol-fed rabbits

The effect of dietary restriction (half of the control ration) on VLDL turnover was investigated in cholesterol-fed rabbits. Rabbits on standard, cholesterol and restricted cholesterol diets were injected with homologous 125I-labelled VLDL. Accompanying the amplification of hypercholesterolemia, additional disturbances of VLDL turnover were observed when cholesterol feeding was associated with dietary restriction. Cholesterol-fed rabbits with normal caloric ration exhibited delayed clearance of 125I-labelled apolipoprotein B component of VLDL compared to control rabbits. This was markedly accentuated in underfed rabbits, indicating further down-regulation of apolipoprotein B,E receptors in these animals. Furthermore, a reduced proportion of radiolabelled apolipoprotein B was converted from VLDL to intermediate-density lipoprotein (IDL) and LDL in both groups receiving cholesterol-rich diets. Thus, the combination of further impairment in plasma clearance of VLDL and the poor conversion into IDL and LDL could account for the massive increase of beta-VLDL in underfed animals on cholesterol-rich diets.     

The ultrastructure of Encephalitozoon cuniculi growing in renal tubules of rabbits

A wild type rabbit infected orally with cell culture-grown Encephalitozoon cuniculi. Twelve weeks after infection the rabbit was killed and blocks of kidney tissue were fixed for histology and electron microscopy. E. cuniculi were observed within kidney collecting tubule cells. The ultrastructure and development of E. cuniculi in these cells was similar to that described in cultured cells and peritoneal macrophages.     

Age-related relationships between muscle fat content and metabolic traits in growing rabbits

This study was aimed at ascribing muscle fat accretion in growing rabbits to changes in several extra-muscular and intra-muscular metabolic pathways. At 10 wk or 20 wk of age (n = 8 per group), tissue lipid content and metabolic indicators of nutrient anabolic or catabolic pathways were simultaneously assessed in the liver, perirenal fat, the heart and the Longissimus lumborum (LL) muscle, together with plasma concentrations in energy-yielding metabolites. Lipid content significantly increased with age (P < or = 0.01) in the glycolytic LL muscle (+67%) and the oxidative heart (+30%). In the former muscle, it was statistically correlated (r2 = 0.68; P < 0.01) to the changes in the orientation of muscle metabolism towards an enhanced lipogenic capacity and a depressed capacity for fatty acid transport and nutrient oxidation, and to indications of lower availability in plasma glucose and triglycerides. In the heart, age-related fat accretion was positively associated (r2 = 0.48, P < 0.01) to intrinsic metabolic changes towards an enhanced lipogenic capacity, together with a lower availability in plasma glucose. Variables representative of cardiac catabolic capacity tended to be negatively correlated to fat content in the heart (r2 = 0.15, P = 0.07). In growing rabbits, muscle fat content variation was proven to result from a reciprocal balance between catabolic and anabolic fatty acid fluxes, rather than to be assigned to one specific energy metabolic pathway.     

Effect of rabbit doe-litter separation on 24-hour changes of luteinizing hormone,follicle stimulating hormone and prolactin release in female and male suckling pups

Background  

The daily pattern of nursing of the rabbit pup by the doe is the most important event in the day for the newborn and is neatly anticipated by them. Such anticipation presumably needs a close correlation with changes in hormones that will allow the pups to develop an appropriate behavior. Although a number of circadian functions have been examined in newborn rabbits, there is no information on 24-h pattern of gonadotropin release or on possible sex-related differences in gonadotropin or prolactin (PRL) release of pups. This study examined the 24-h changes of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) in 11 days old suckling female and male rabbits left with the mother or after short-term (i.e., 48 h) doe-litter separation.     

Effects of naloxone or transient weaning on secretion of LH and prolactin in lactating sows

Sows (N = 16) were infused intravenously for 8 h with saline or naloxone (200 mg/h) or their litters were transiently weaned for 8 h. Before infusion, 200 mg naloxone were administered to elevate quickly concentrations of naloxone. Blood samples were collected from sows at 15 min intervals for 24 h, beginning 8 h before and continuing until 8 h after imposition of treatments during the middle 8-h segment. Frequency of episodic release of LH and concentrations of prolactin were similar before, during and after infusion of saline. Average concentration of LH was greater during the last than during the middle 8-h segment when sows were given saline. Frequency of episodic release of LH increased and concentrations of prolactin decreased during infusion of naloxone or transient weaning; however, average concentration of LH increased during transient weaning, but not during infusion of naloxone. After transient weaning or infusion of naloxone, frequency of release of LH decreased, returning to pretreatment values in sows infused with naloxone but remaining above pretreatment values in sows subjected to transient weaning. At the resumption of suckling by litters in sows subjected to transient weaning, prolactin increased to levels not different from those observed during the 8-h pretreatment segment. Prolactin did not increase until 4-5 h after cessation of naloxone infusion. We conclude that continuous infusion of naloxone altered secretory patterns of LH and prolactin. Collectively these results provide evidence that the immediate effects of weaning on LH and prolactin in sows are mediated in part through a mechanism involving endogenous opioid peptides.     

Sperm separation attempts via the use of albumin gradients in rabbits

The objective of this study was to evaluate the sedimentation method using albumin gradients to determine whether it could help pre-select sex in rabbits. Of the 21 litters produced during natural mating, the sex ratio was 52.8% males which did not differ (P>0.05) from 55.3% males (nine litters) produced via AI from semen recovered after sedimentation through albumin gradients. The results obtained in this study are consistent with some but not all previous data. The quality of the recovered spermatozoa improved (P<0.05) when compared to those in the whole ejaculate. The sex ratio results obtained in this study suggest that sedimentation methods via the use of albumin gradients may not be effective for separating X and Y spermatozoa. Furthermore, actual sex ratio data should be stressed in all future studies with X and Y sperm separation, in addition to the $\text{in}$$\text{vitro}$ data generated.     

Immunofluorescence location using monoclonal antibodies of prolactin receptors in mammary epithelial cells of lactating rabbits

Immunofluorescent staining of PRL receptors on frozen sections of lactating rabbit mammary gland with a monoclonal antibody (IgG1 M110) shows that receptors are localized in the cytoplasm of epithelial cells and on short portions of plasma membrane. In vivo treatment by bromocriptine or in vitro treatment of mammary tissue slices by monensin modifies localization of receptors.