Australian journal of biological sciences最新文献

The temperature and humidity of expired air from three adult Merino sheep were measured at air temperatures of 20, 30 and 40 degrees C before and after the animals were shorn. Expired air was apparently always saturated with water vapour. At the higher air temperatures the temperature of expired air was close to deep body temperature; at lower air temperatures, expired air had been significantly cooled, e.g. to 32.3 degrees C in shorn sheep at 20 degrees C air temperature. Expired air was cooler from shorn than from unshorn animals at 20 and 30 degrees C air temperature, possibly due to thermally induced vasomotor changes in the upper respiratory tract. Cooling of expired air would be expected to lead to recovery of some of the water evaporated during inspiration; at 20 degrees C air temperature, this fraction was estimated to be 25% in unshorn sheep and 36% in shorn sheep.

Variability in different lots of commercial serum albumin affects mammalian embryo development in culture. The composition of commercial preparations of ovine, bovine and defatted bovine serum albumin and a fraction of ovine serum containing proteins with a mean molecular weight of 65 kDa (fraction 3) was examined by polyacrylamide gel electrophoresis. All preparations were heavily contaminated with serum proteins other than albumin. Day-6 sheep morulae were cultured for 48 h in a basal bicarbonate-buffered salt solution supplemented with the commercial preparations of ovine, bovine or defatted bovine serum albumin. These three albumin preparations differed in their abilities to support the development of morulae into expanded blastocysts, but these differences disappeared when the basal medium was also supplemented with a component of ovine serum containing substances with molecular weights of less than 10 kDa. In the latter case, the three commercial albumin preparations and fraction 3 of ovine serum all supported full development in about 40-60% of morulae.

Evidence was cited to show that: (1) prostacyclin (PGI2) plays a luteotrophic role in the bovine corpus luteum and that products of the lipoxygenase pathway of arachidonic acid metabolism, especially 5-hydroxyeicosatetraenoic acid play luteolytic roles; (2) oxytocin of luteal cell origin plays a role in development, and possibly in regression, of the bovine corpus luteum; and (3) luteal cells arise from two sources; the characteristic small luteal cells at all stages of the oestrous cycle and pregnancy are of theca cell origin; the large cells are of granulosa cell origin early in the cycle, but a population of theca-derived large cells appears later in the cycle. Results of in vitro studies with total dispersed cells and essentially pure preparations of large and small luteal cells indicate that: (1) the recently described Ca2+-polyphosphoinositol-protein kinase C second messenger system is involved in progesterone synthesis in the bovine corpus luteum; (2) activation of protein kinase C is stimulatory to progesterone synthesis in the small luteal cells; (3) activation of protein kinase C has no effect on progesterone synthesis in the large luteal cells; and (4) protein kinase C exerts its luteotrophic effect in total cell preparations, in part at least, by stimulating the production of prostacyclin. The protein kinase C system may cause down regulation of LH receptors in the large cells.

Electrophoretic examination (isoelectric focusing and polyacrylamide gel electrophoresis) of 157 plasmas from a Kangaroo Island population of tammar wallabies (Macropus eugenii) resulted in the identification of five putative condominant protease inhibitor alleles, F, I, M, P and S, which exhibited microheterogeneity due to variable terminal sialic acid content. The frequencies of the five alleles in this population were 0.041(F), 0.682(I), 0.194(M), 0.073(P) and 0.010(S). The proteins had isoelectric points in the pH range 3.94-4.38, Mr of 60,500 to 66,000 and were identified as protease inhibitors by their abilities to inhibit both trypsin and chymotrypsin. Protein blotting of the denatured proteins demonstrated cross reaction with antiserum to human alpha 1-protease inhibitor.

Fetal and placental growth, and fetal and maternal urea synthesis in late gestation, were studied in 2-year-old Corriedale ewes on a maintenance ration (M) except when subjected to moderate dietary restriction from day 50 to day 100 (RM), day 100 to day 135 (MR) or day 50 to day 135 (RR). In comparison with fetuses of ewes maintained throughout the experiment (MM), RR fetuses were smaller and RM fetuses were larger whereas MR fetuses were unaffected; all restrictions were associated with increased placental size. Fetal urea synthesis at day 133 in the well-nourished ewes (MM) was 21.5 mg N h-1 kg-1 increasing to, respectively, 25.7, 27.3 and 38.8 mg N h-1 kg-1 in groups MR, RM and RR; these values were 1.6, 3.9, 2.2 and 3.8 times the maternal rates of synthesis. On the basis of the observed urea synthesis rates, amino acid oxidation could have accounted for up to, respectively, 32, 38, 40 and 57% of fetal oxygen consumption in groups MM, MR, RM and RR. Amino acids, in addition to their role in tissue accretion, may be key energy substrates for the fetus.

The ductuli efferentes testis of the rat form a cord which is embedded in adipose tissue. The cord is anatomically differentiated into a proximal cylindrical region, the initial zone, and an ampulla, the coni vasculosi. The initial zone contains six or seven ductuli which leave the rete testis and run in a sinuous path, roughly parallel with one another. However, the ductuli in the coni vasculosi are more sinuous than in the initial zone and they anastomose; pairs join together to form ultimately a single, common ductulus efferens. Stereological studies of paraffin sections and electron micrographs showed that the differentiation of the ductuli into two parts can be recognized at tissue and cellular levels of organization. Stereological and micropuncture studies showed that the ductuli efferentes reabsorb most of the fluid leaving the testis and it was concluded that most reabsorption occurred in the initial zone. It was estimated that the rate of fluid absorption is greater in the ductuli efferentes than in the proximal convoluted tubules of the kidney. The mechanism of fluid transport across the mucosa of the ductuli is considered in the Discussion. It is concluded that transport in vesicles and vacuoles could not account for the rate of fluid reabsorption and that the main mechanism of transport probably involves the coupling of water and active salt transport.

The role of circulating, non-esterified, long-chain fatty acids (NEFA) as a source of energy for the whole animal and skeletal muscle was investigated in fed non-pregnant sheep at rest and during exercise. Infusion of tracer quantities of [1-14C]oleic or [1-14C]stearic acid was combined with the use of arteriovenous difference studies on fed sheep at rest or during a 2 h period of exercise on a belt treadmill moving at 4.5 km h-1. At rest all parameters of NEFA metabolism indicated a minimal role for oxidation. Thus the concentration in plasma (0.07 +/- 0.01 mmol l-1), entry rate (0.08 +/- 0.02 mmol h-1 kg-1 body wt), contribution to whole animal oxidation (1.2 +/- 0.3%) and utilization of NEFA by skeletal muscle (0.046 +/- 0.008 mmol h-1 kg-1 muscle) were all low. Exercise prompted a shift to lipolysis and accordingly the above parameters increased markedly some 13-24-fold. The circulating concentration of ketone bodies showed only a small increase during exercise and consequently the role of ketone bodies as an energy source during exercise was minimal. Glucose utilization by skeletal muscle was considerable in animals at rest and it represented the most significant potential fuel of skeletal muscle. Exercise resulted in a sustained increase of 3-4-fold in the utilization of glucose by skeletal muscle. Thus the traditional view that NEFA and not glucose is a predominant fuel of skeletal muscle of fed sheep should be appraised.

Computerized gas chromatography-mass spectrometry was used to measure precisely the hypothalamic levels of noradrenaline (NA), dopamine and serotonin together with those of their major neuronal metabolites 3,4-dihydroxyphenylethyleneglycol (DHPG), 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid in normal male rats 45 min after stimulation of hypothalamic-pituitary-adrenal function by urethane (1.3 g/kg) administration. Urethane treatment resulted in a significant elevation of central noradrenergic neuronal activity (NNA) as assessed from marked rises in hypothalamic DHPG concentrations and the ratio (DHPG/NA). At the same time there was significant stimulation of ACTH and corticosterone release and inhibition of growth hormone release. These hormonal and central effects of urethane (but not anesthesia) were inhibited when the alpha 2-agonist clonidine (150 micrograms/kg) was co-administered. Urethane had no major effect on hypothalamic dopamine or serotonin status. We propose that the release of ACTH and the suppression of growth hormone release following urethane anaesthesia is a result of activation of central NNA and suggest that the hormonal responses are mediated via hypothalamic noradrenergic facilitation of corticotrophin releasing factor and somatostatin release to the anterior pituitary.

Two distinct activator proteins for lipoprotein lipase (LPL) have been isolated in approximately equal amounts from ovine plasma. These low molecular weight proteins were readily separated from each other on the basis of size and charge. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated proteins of Mr about 8000 and 5000, with pI in urea-containing gels of about 5.1 and 4.8 respectively. Each of the ovine activator proteins was as effective as human apolipoprotein C-II (apo C-II) in activating LPL, with 1 microgram/ml giving near to maximum activation, and in lowering the apparent Km of LPL for triolein substrate. As the ratio of activator to triolein increased from 0.16 to 5.2 (micrograms/mg) the apparent Km fell from about 0.5 to 0.18 mM. Whereas human apo C-II and the two ovine activators were equally effective in stimulating the hydrolysis of triolein, differences were observed between the human and ovine activators when p-nitrophenylbutyrate was used as substrate. Unlike human apo C-II, which produced significant inhibition of p-nitrophenylbutyrate hydrolysis, the ovine activators were without effect. This suggests that the interaction between the ovine activators and LPL is different from that of human apo C-II.