The effects of short-term exposure to high ambient temperatures on gas exchange, heat production (HE), respiration rate (RR) and rectal temperature were evaluated individually with boars of approximately 100 kg live weight. The boars were of different breeds with four of Yorkshire (YS), eight of Danish Landrace (DL), out of which three were found stress susceptible by the halothane test (DLH + ), eight of Duroc (DR) and eight of Hampshire (HS) breeds. After 1 h rest in the respiration chamber at 17-0°C the gas exchange measurements started with al-h basal period at 17 °C, followed by 2h of heating during which temperature increased to 35-0 °C (period I) and then further to 39-7X1 (period II). Then cooling of the chamber started, and after 1 h (period III) temperature had decreased to 21-8°C, and after the 2nd h of cooling (period IV) temperature was 18-2 °C. The gas exchange was measured for each hour from 09.00 h (basal period) until 14.00 h (period IV). RR was recorded every 15 min. Rectal temperatures were measured when the animals were removed from the chamber. The gas exchange and HE increased slowly during period I but rapidly in period II, followed by decreasing values in the cooling periods. HS and DLH + had considerably higher gas exchange and HE than other breeds in these two periods and the values remained high during period III. In period IV all breeds had gas exchange rates and HE below those of the basal period. RR increased slightly in period I and then a sharp increase followed during period II. Maximum RR was recorded in period III with an average of 183 breaths per min for all breeds. RR increased earlier and more steeply in HS and reached the highest mean value of 236 breaths per min. Four HS boars salivated heavily during heat stress and rectal temperatures of these animals were 39-7 °C when removed from the chamber compared with close to 39-0 °C for all other breeds. It was concluded that there were considerable breed differences in response to heat stress and that DLH + and HS were more severely stressed than boars ofYS, DL and DR.
Experimental examination of hypertonic glucose solutions injected into small intestinal sections from live pigs and aspirated 15 minutes later showed the following:
The volume of a hypertonic glucose solution increases parallel with increasing length of the section of the jejunum into which the solution is diffused.
The amount of sodium and chloride seeping in with the water during the experimental 15-minute-periods is equal to the rise in volume and thus the amounts of sodium and chloride seeping in vary with the size of the area of the mucous membrane on which the 50 ml of a 50% glucose solution is diffused. Not only the amount but also the concentration of sodium and chloride in the aspirates increases considerably when the intestinal sections are prolonged from 100 to 200 cm. A further prolongation rather impedes the increase in concentration.
The volume, i.e. the sodium and chloride content of the transuded fluid, is uniform in at least six successive experiments in which the same intestinal section is exposed.
The valuation of results from the potassium analyses cannot be quite as clear- cut, probably because of a certain admixture of blood corpuscles.
In repeated experiments the protein concentration rises in the fluid in the intestinal lumen and a pronounced oedema of the intestinal wall and the mesentery is noted.
Experiments in which isolated pig intestines were used showed the following :
(1) GOT, GPT, and LDH are demonstrable in abundance in the liquid recovered from intestines which have been exposed to the action of 50 ml of a 50% glucose solution for 15 min following washings with isotonic glucose solutions.
(2) If intestines were exposed to a 50% glucose solution for 4—6 consecutive 15- minute-periods the concentration of enzymes in the liquid recovered would fall.
(3) Enzyme electrophoretic investigations of LDH in plasma, in the intestinal content, and in the mucous membrane of the intestine, indicate that the LDH present in the intestinal liquid originates from the intestinal mucous membrane.
(4) The presence of GOT, GPT, and LDH in the intestinal liquid may be considered a secretion or diffusion of these enzymes into the intestinal lumen and not exclusively as indicators of cell damage.
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