Australian journal of biological sciences最新文献

During the course of a study of the control of expression of steroid-binding proteins in human mammary cancer oestrogen sulfotransferase was isolated from bovine placenta. By a combination of salt precipitation and ion-exchange and gel-permeation chromatography two forms of the enzyme were isolated. The forms, which apparently differ only in charge, have specific activities 100-300 times greater than has previously been reported for the enzyme. Partial peptide sequences of these enzymes are presented.

In order to extend comparative mapping studies to the monotreme mammals (subclass Prototheria), somatic-cell hybrids were obtained between Chinese-hamster cells deficient in hypoxanthine phosphoribosyltransferase (HPRT) and platypus fibroblasts. The characteristics of these hybrids closely resemble those of metatherian x eutherian hybrids, in that they are recovered at low frequency and they rapidly segregate and fragment platypus chromosomes. Biochemical and cytological studies of the hybrids, their subclones and HPRT-deficient revertants indicate that phosphoglycerate kinase is syntenic with HPRT in the platypus (as it is in other mammals); however, the studies do not permit chromosomal assignment of the syntenic group. The implications of the chromosomal location of this ancient synteny group for the evolution of the mammalian X chromosome are discussed.

The availability and utilization of cystine and methionine were measured in single-bearing Merino ewes on three occasions, approximately 90, 110 and 130 days after mating, and the effects on these traits of sulfur amino acids (SAA) infused into the abomasum were also measured. Two levels of SAA were infused containing 0.5 or 1.0 g day-1 organic sulfur with DL-methionine contributing two-thirds and L-cystine one-third of the supplementary sulfur. The quantity of the diet offered was increased at each occasion so as to maintain maternal liveweight. The rates of irreversible loss of both cystine and methionine from plasma increased as pregnancy advanced, but the ratios between the rates of irreversible loss and intake of digestible organic matter (DOMI) did not vary with stage of pregnancy. The average daily rates of irreversible loss of cystine and methionine by the ewes consuming the diet alone were 13.6 and 119 mmol kg-1 DOMI respectively. The average rates of irreversible loss of methionine (Im, mmol h-1) and of cystine (Ic, mmol h-1) were both linearly (P less than 0.05) related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): Im = 2.44 (+/- 0.33) s + 1.28 (+/- 0.13); and Ic = 0.16 (+/- 0.02) s + 0.30 (+/- 0.01). Five per cent of the rate of irreversible loss of cystine arose from trans-sulfuration of methionine by ewes consuming the ration only, but greater percentages (14 and 22%) were observed when the ration was supplemented with SAA (P less than 0.05). These transfer quotients were not influenced by stage of pregnancy. The stage of pregnancy did not influence the concentration of cystine or methionine in the plasma, but the abomasal infusions of SAA significantly increased the concentration of both SAA. The ewes consuming the basal diet were in positive balance for both nitrogen and sulfur. The retention of nitrogen did not vary with stage of pregnancy (average (s.e.), 5.8 (0.9) g day-1), but that of sulfur increased from 0.6 to 1.0 and 1.3 g day-1 in periods 1, 2 and 3, respectively (P less than 0.05). The retentions of nitrogen (N, g day-1) and of sulfur (S, g day-1) were linearly and significantly related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): N = 2.7 (+/- 0.7)s + 4.4 (+/- 0.3); and S = 0.49 (+/- 0.03)s + 0.72 (+/- 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Twice daily intradermal (ID) injections of mouse epidermal growth factor (mEGF) in sterile saline for 1-4 days into delineated areas of skin of Merino sheep produced dose-dependent changes in wool follicles and fibres, ranging from slight reduction in follicle bulb size and transient disturbance of cuticle formation on some fibres to the induction of catagen of follicles and shedding of fibres with distorted, tapered ends. Regeneration of follicles commenced by day 7. By contrast, ID injections of saline did not affect follicle activity. The epidermis became thicker and more parakeratotic after multiple injections of mEGF than after injection of saline, but was almost normal again by day 14. Persistent small increases in sebaceous gland size, additional to those induced by ID injections of saline, and delayed small increases in sweat gland size also occurred after multiple injections of mEGF. Daily topical applications of mEGF in 50% (v/v) aqueous propylene glycol 5 days each week for 4 weeks did not affect wool growth or the follicles and other skin components. The only effect observed, due to application of the aqueous propylene glycol, was an increase in the number of layers of cornified cells in the stratum corneum of the epidermis, with the cells arranged in clearly discernible stacks. The effects produced by ID injections of mEGF indicate that mEGF acts directly on the pilosebaceous and epidermal components of skin.

The pattern of ovulation of Merino ewes was studied by repeated laparoscopy each 14 days in the anoestrous (n = 97) and breeding (n = 87) seasons. In the anoestrous season the proportion of ewes ovulating did not decrease below 11%, 42% of ewes never ovulated and the remainder fluctuated between the two states. On 20 occasions a clear anovulatory period was interrupted by an isolated spontaneous ovulation. In the breeding season the overall mean proportion of ewes with corpora lutea or albicantia at laparoscopy was 87%, 54% of ewes ovulated regularly throughout while in another 31% absence of corpora lutea or albicantia coincided with the follicular phase of an oestrous cycle as evidenced by an appropriately aged corpora lutea at the next laparoscopy. Of the remaining 15% of the flock 3% had anovulatory periods greater than 14 days while the remainder experienced irregular ovulatory cycles--the majority due to short periods of anovulation but some ewes retained corpora lutea for longer than 14 days while others ovulated twice between successive laparoscopies.

After intravenous administration of alloxan (50 mg kg-1 liveweight) to lactating ewes, there were triphasic changes in plasma glucose and insulin. Almost immediately, plasma insulin decreased and hyperglycaemia occurred, then, between c. 5-12 h, insulin increased and ewes became hypoglycaemic. Thereafter, insulin decreased and glucose increased from c. 20 h after alloxan and the diabetic state was established. Changes in glucose production and utilization correlated with changes in plasma glucose. Exogenous insulin was administered from 30 h after alloxan, and it took some 2 weeks to stabilize ewes. During this period, when mild hyperglycaemia persisted, milk yields and feed intakes were decreased but milk fat content was elevated. Once ewes were stabilized, plasma glucose, milk yield, feed intake and milk fat content returned to levels prior to alloxan. These observations are consistent with insulin playing a role in the aetiology of the 'low milk fat syndrome' in the ruminant. It appears that the alloxan-treated, insulin-stabilized ewe would be a useful model for studying the role of insulin during lactation, but it is necessary to allow time for animals to overcome effects of administration of alloxan.