Differential induction of rat hepatic cytochrome P-448 and glutathione S-transferase B messenger RNAS by 3-methylcholanthrene

Liver poly(A⁺)-RNA isolated from untreated and 3-methylcholanthrene treated rats has been translated in the rabbit reticulocyte cell-free system in order to determine the level of translationally active cytochrome P-448, glutathione S-transferase B and serum albumin mRNAs. Translatable cytochrome P-448 mRNA was not detected in untreated rats; however in animals treated with 3-methylcholanthrene cytochrome P-448 mRNA was elevated markedly. Functional rat liver glutathione S-transferase B mRNA was elevated 2-fold by 3-methylcholanthrene administration, whereas the serum albumin mRNA level was decreased by 50%. Our results indicate that 3-methylcholanthrene is not just a specific inducer of drug metabolizing enzymes but can alter the mRNA level encoding other polypeptides and thus affect cellular homeostasis.     

A procedure for the fusion of cells in suspension by means of polyethylene glycol

The nuclei of chick and human fibroblasts are readily distinguishable in Leishman stained heterokaryons. The use of these two types of cell has allowed development of a method for fusion in suspension based on the use of polyethylene glycol (PEG) of MW 1000 in Dulbecco's medium containing 15% dimethylsulfoxide (DMSO).     

Morphology,histochemistry and physiology of the major salivary glands in the echidna Tachyglossus aculeatus (Monotremata)

The three major salivary glands of the monotreme echidna are described. The parotid is a typical serous gland with tubulo-acinar secretory endpieces and a well-developed system of striated ducts. The mandibular gland, although light microscopically resembling a mucous gland, secretes very little glycoprotein. Its cells are packed instead with serous granules, resembling in fine structure the “bull's eye” granules in the mandibular gland of the European hedgehog Erinaceus europaeus. The sublingual glands secrete an extremely viscous mucous saliva. Expulsion of this saliva through the narrow ducts is probably aided by contraction of the extensive myoepithelial sheaths surrounding the secretory tubules. Application of the glyoxylic acid induced fluorescence method failed to demonstrate adrenergic innervation in any of the glands.     

Effects of acute and prolonged exposure to heat on regional blood flows in pregnant sheep

This study deals with fetal growth retardation in heat-exposed sheep, and provides information on mechanisms of acclimation to heat. Radioactive microspheres were used to measure regional capillary blood flows in conscious sheep 80-100 days pregnant, at first in a thermoneutral environment, next after 2.5-6 h exposure to a hot environment of 40 degrees C, 25 mmHg water vapour pressure, and then 7 days and 15-20 days later, after spending 9 h daily in the heat. Maternal blood flow in the placental cotyledons was decreased by the first heat exposure, and remained depressed during the period of periodic heating. Reduction in placental blood flow on the maternal side could be part of the mechanism by which fetal development is retarded in heat-stressed sheep. Acclimation to heat was indicated by a decrease in the rate of rise in rectal temperature during the first 2 h of daily exposure to heat. Concomitantly, there was a progressive increase in the blood flow in extremity skin and nasal mucosa, which are tissues concerned with facilitation of heat loss during acute heat stress. However, in respiratory muscles which are also concerned with heat-loss, there was no further increase in flow after the initial response to to acute heat, indicating that heat acclimation is not due to an increased ability to pant. Blood flow in other tissues such as gut, pancreas and adipose tissue progressively decreased. These changes in blood flow have possible adaptive significance.     

Heat-shock induced tolerance to the embryotoxic effects of hyperthermia and cadmium in mouse embryos in vitro

Mammalian embryos growing in vitro are harmed by short elevations in the culture temperature. However, a relatively mild hyperthermic exposure can induce thermotolerance, a transient state of resistance to the effects of a subsequent heat exposure. The present study examines the induction of tolerance to heat and cross-tolerance to another teratogen, cadmium, in day 8 CD-1 mouse embryos in vitro. The ability of a mild heat pretreatment (5 min at 43 degrees C) to partially protect embryos against an embryotoxic heat exposure (20 min at 43 degrees C) was demonstrated. The frequency of death was reduced from 43% to 20%, abnormal branchial arches from 44% to 13.2%, and retarded turning from 22% to 5% in pretreated embryos. Other malformations, such as small forebrains and microphthalmia, were not affected, and the rate of exencephaly was significantly increased. The same heat pretreatment (5 min at 43 degrees C) was also found to reduce the damaging effects of a subsequent exposure to 1.75 microM cadmium. In the absence of pretreatment, cadmium caused 55% embryo deaths and 87% malformations, but prior heat exposure caused significant reductions in these frequencies to 29% and 55%. The total morphological score was higher in the pretreated group, as were the measurements of the yolk sac diameter, crown-rump length, and head length. Thus, embryos that have developed resistance to hyperthermia are also partially protected against the harmful effects of a second teratogen, cadmium. The response of the embryo to elevated temperatures may be involved in the development of tolerance to a variety of stresses.