Katarina Cvek

Housing-related activity in rats: effects on body weight, urinary corticosterone levels, muscle properties and performance

The cage systems commonly used for housing laboratory rats often result in sedentary and overweight animals, as a consequence of restricted opportunities for physical activity combined with ad libitum feeding. This can have implications both for animal well-being and for the experimental outcome. Physical activity has several known positive effects on health and lifespan, and physical fitness might therefore be incorporated into the animal welfare concept. The aim of this study was to investigate if and how pen housing affects the physical activity and fitness of rats. Thirty-two juvenile male Sprague-Dawley rats were randomly assigned to two different housing systems for a 4-week period. Sixteen rats were kept individually in standard Makrolon type III cages (42 × 26 × 18 cm) furnished with black plastic tubes (singly-housed, SI). The remaining rats were kept in groups of eight, housed in large floor pens (150 × 210 cm), which were furnished with various objects to increase environmental complexity (pen-housed, PH). The body weight gain, and food and water intake of the rats were measured. During weeks 3 or 4, home cage behaviour, urinary cortiosterone/creatinine ratios (CO/CR), and muscle strength on an inclined plane, were measured. Enzyme activities and glycogen content were measured in tissue samples from m. triceps brachii taken after euthanization at the end of the study. There were no significant differences between groups for food and water intake, but PH rats weighed 14% less than SI rats after 4 weeks, and PH rats also had a more diverse behavioural pattern than SI rats. PH rats had significantly higher oxidative capacity (28% more citrate synthase (CS)) and greater glycogen content (28%) in their muscle samples than SI rats. The PH rats performed significantly better on the inclined plane, both in the muscle strength test (mean angle 75 ± 0.5° for PH rats and 69 ± 0.4° for SI rats) and the endurance strength test (mean time 233 ± 22 s for PH rats and 73 ± 14 s for SI rats). There was a negative correlation between body weight and results on the inclined plane for the PH rats. There were no significant differences between housing types with respect to CO/CR ratios. In conclusion, the large pen represents an environment that stimulates physical activity and more varied behaviour, which should be beneficial for the welfare of the animal.

Localization of carbonic anhydrase in the goat mammary gland during involution and lactogenesis

The aim of this study was to determine whether carbonic anhydrase (CA) activity in goat mammary capillaries is regulated mainly by local or systemic mechanisms. One gland was dried before the contralateral gland, and after parturition only one gland was milked. Biopsies were taken from the mammary glands of three goats at 14 d intervals during involution and the start of the following lactation. A histochemical method was used to visualize sites of CA activity. To follow the involution process, milk (liquid) samples were taken from both teats each week and analysed for pH and composition. The time course of CA activity disappearance and reappearance in the capillaries was related to changes in milk composition and alveolar area. A dense network of capillaries showing membrane-bound staining for CA was found surrounding the alveoli in the lactating gland. CA activity gradually decreased in the drying gland, although the other gland was being milked. After 8 weeks involution the dried gland had a significantly lower number of stained capillaries than the milked gland. Almost no stained capillaries were found during late pregnancy, when both glands were dried and the tissue growth maximal. During lactation milk pH was 6.6 +/- 0.3 and this increased to 7.0 +/- 0.1 in the course of involution. In the last trimester of pregnancy the pH returned to its lower value, while the mammary gland was devoid of stained capillaries. Therefore, the capillary CA could not have been directly involved in the pH regulation of milk. The CA activity reappeared in the capillaries directly after delivery, but only in the milked gland. Clearly the regulation of CA activity is influenced more by local than by systemic factors and is associated with the metabolic activity of milk secretion.

REPRODUCTIVE PERIOD AFFECTS WATER INTAKE IN HEAT-STRESSED DEHYDRATED GOATS

Water intake following dehydration was studied in pregnant (N = 5), lactating (N = 4) and nonpregnant, nonlactating (N = 5) Swedish domestic goats (Capra hircus) to investigate if reproductive period affected drinking. Plasma cortisol concentration and the hematocrit value were measured to evaluate stress. The goats were water deprived from 9.00 h until 15.05 h the next day. They were fed at 7.00 and 15.20 h. On the second day, ambient temperature was increased from 20 degrees C to 38-39.5 degrees C for 5.15 h to accelerate water losses. Water temperature during rehydration was 35 +/- 1 degree C. Plasma Na concentration and osmolality increased most in dehydrated and heat-stressed pregnant and lactating goats. Pregnant goats lost 2.2 kg of their body weight. They drank 3.5 l immediately, followed by 2.5 l during afternoon eating. Lactating goats lost 4.9 kg and drank 6.3 l at once, and 3.9 l during feeding. Nonpregnant, nonlactating goats lost 1.7 kg and drank 2.6 l followed by 0.6 l. The large water consumption in pregnant and lactating goats caused hyponatremia and hemodilution, but they continued to drink during the night (0.5 +/- 0.2 l and 0.8 +/- 0.5 l, respectively). Renal free water clearance increased in all periods, with a long-lasting water diuresis during pregnancy. Plasma cortisol concentrations and the hematocrit values rose in connection with water intake. These results imply that the thirst center became less sensitive to inhibitory signals from the oropharyngeal tract and the diluted blood plasma during pregnancy and lactation. Catching sight of water was the most exciting procedure during these experiments.

Preference for drinking warm water during heat stress affects milk production in food-deprived goats

Food deprivation leads to diminished water intake and decreased milk production in lactating goats. The aim of this study was to determine whether these effects could be alleviated by offering six lactating goats (Capra hircus) warm water to drink at normal or hot ambient temperatures. The food deprivation period was started on Day — 1 at 0700 h by feeding the goats hay but no concentrates. No food was then given until 1515 h on Day 0. Between 0700 and 1800 h on Day 0 water was supplied to the goats in three different ways at different ambient air temperatures as follows: (1) cool (15 °C) water in one bucket and warm (35 °C) water in another (cool-warm water experiment); (2) cool (15 °C) water in two buckets (cool-cool water experiment); and (3) warm water in one bucket and cool water in the other in combination with a hot ambient temperature from 1045 h to 1700 h (heat-stress). Experiments 1 and 2 were performed at room temperature (17.5–19 °C) and at a relative humidity of 60–70%. In Experiment 1, the goats drank 0.7 ± 0.6 1 of the cool water and 5.0 ± 1.2 1 of the warm water before re-feeding (P < 0.001). In Experiment 2, the goats drank 1.5 ± 0.6 1 of the cool water. In Experiment 3, they drank more warm water (4.1 ± 0.8 1) than cool water (0.51 ± 0.2 1; P < 0.001). Body weight decreased in all experiments during Day — 1. It decreased further on Day 0 in Experiment 2, but not in Experiment 1, and in Experiment 3 the goats regained their pre-starvation body weight. The milk lactose concentration fell by 10 and 11 mmol l−1 in Experiments 1 and 2, respectively (P < 0.001, afternoon Day — 2 compared with afternoon Day 0), but only by 2 mmol l−1 in Experiment 3 (NS). The mean milk K concentration decreased by 7, 8 and 4 mmol l−1 in Experiments 1, 2 and 3, respectively. The milk Na concentration did not change in any of the experiments. Milk osmolality did not change despite the drop in milk lactose and K concentrations. Food deprivation reduced milk flow in all experiments, which resulted in decreased secretions of lactose and protein in all experiments. The fat secretion did not decrease significantly during the heat-stress experiments. It is concluded that offering warm instead of cool drinking water to food-deprived lactating goats increased their water consumption and that this, in combination with heat stress, counteracted the reduction of the milk secretion.

Functional receptors for atrial natriuretic peptide in the rat mammary gland during lactation.

The present study was undertaken: 1) to localize and characterize atrial natriuretic peptide (ANP) receptors in the rat mammary gland; and 2) to elucidate ANP-induced cellular formation of cyclic GMP (cGMP) and alterations in alveolar morphology during both early and late lactation. Receptor autoradiography, employing rat-specific[ 125I]ANP as radioligand, demonstrated binding sites in the secretory tissue and larger blood vessels of the mammary gland. Binding of [125I]rANP to membrane fractions was completely displaced by unlabeled ANP and brain natriuretic peptide. C-type natriuretic peptide and cANP(4–23) revealed limited competition with radiolabeled ANP only during early lactation, indicating a more heterogenous receptor population at that time. Systemically administered ANP induced cGMP formation in the alveolar epithelium, as shown with immunohistochemistry, and increased mammary tissue cGMP concentrations in vivo throughout the lactation period. Image analysis revealed enlargement of alveolar (but...

Evolution of the mammary capillary network and carbonic anhydrase activity throughout lactation and during somatotropin treatment in goats

During the normal course of lactation, mammary metabolic activity and blood flow are closely correlated. Six lactating goats were used in this experiment to test the hypothesis that the capillary network and the capillary enzyme, carbonic anhydrase (CA; EC 4.2.1.1) are important regulatory factors involved in the coordination of mammary blood flow (MBF) and metabolic activity. Milk vein blood velocity was determined as a measure of MBF, and fine needle mammary biopsies were obtained at different time points during lactation and by the end of a 14-d bovine somatotropin (BST) treatment initiated 3 months post partum. In mammary sections, CA activity was determined histochemically and alveolar and capillary structures by image analyses upon azure blue staining. In early lactation, alveoli were large and surrounded by many small capillaries with high CA activity. As lactation progressed, capillaries almost tripled in size, whereas number of capillaries surrounding each alveolus decreased by 1/3, and CA activity more than halved. BST treatment did not affect capillary traits but increased number of alveoli in mammary sections, and BST thus appeared to be targeted mostly towards the mammary epithelial cell. Milk vein blood velocity decreased over the course of lactation, when capillary area markedly increased, suggesting that control of mammary blood perfusion is not at the level of the capillary itself, but at pre- or post-capillary sites. We suggest that the observed changes in capillary diameter and CA activity with progressing lactation contributes to reduce efficiency of nutrient and waste product exchange across the capillary-mammary epithelial cell barrier, and this could be an important factor in regulation of mammary (epithelial cell) metabolic activity and lactation performance.