The effects of salbutamol on blood pressure and heart rate in Large White and Pietrain-cross breeds of pig.
The effects of the beta 2-agonist salbutamol, on pig heart rate and blood pressure were evaluated at the expected commercially used concentration of 3 ppm in final feed, and at three times this level. Salbutamol was administered to pigs previously fed on control diet ('naive'), and in a second study to pigs fed 3 ppm salbutamol for 19 days ('acclimatized'). Heart rate and blood pressure were measured in conscious 30 kg pigs before (pre-ingestive), during (ingestive) and after ingestion (absorptive) of feed containing 3 or 9 ppm salbutamol. To assess any interaction with 'stress genotype' pigs, measurements were performed in Large White and Pietrain-cross breeds. The mean preingestive heart rates for the Large White and Pietrain-cross pigs were 127 and 109 beats/min, respectively. The corresponding figures for mean arterial blood pressure were 121 and 122 mmHg. The act of ingesting control feed caused heart rate to rise by 36-39% and blood pressure to increase by 17-27%. During the absorptive phase for 'naive' pigs fed 3 ppm salbutamol in the diet, blood pressure fell 5-11% and heart rate increased 20-24%, reflecting a classical baroreceptor mediated response. At 9 ppm the fall in blood pressure of 5-11% was similar to that at 3 ppm, while the rise in heart rate was larger at 31-38%. The magnitude of the changes at both 3 and 9 ppm was less than that evoked by the act of ingestion, with the exception of the heart rate response in Large Whites at 9 ppm, which was similar. The responses of the two breeds were comparable, indicating that salbutamol is unlikely to exacerbate the cardiovascular responses seen in potentially stress-susceptible pigs. The acute changes elicited by 3 ppm salbutamol during the absorptive phase in 'naive' pigs were abolished or substantially less in acclimatized pigs, implying a tachyphylaxis to the agonist's actions. This was confirmed by 9 ppm of salbutamol increasing heart rate of 'acclimatized' Large Whites to the same degree as 3 ppm in 'naive' counterparts. The desensitization in Pietrain-cross pigs was even more marked with no increase in heart rate produced by 9 ppm salbutamol following acclimatization. These data, combined with the rapid tachyphylaxis of response, indicate that salbutamol at the intended commercial inclusion of 3 ppm will not compromise the cardiovascular stability of the growing pig at rest.
White
D G
DG
Department of Veterinary Medicine and Animal Husbandry, Royal Veterinary College, University of London, Hatfield, Herts, U.K.
Rolph
T P
TP
Wagstaff
A J
AJ
D000064:Acclimatization / Q000187:drug effects; D000420:Albuterol / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003433:Crosses, Genetic; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D013552:Swine / Q000502:physiology*; D013997:Time Factors
D000420:Albuterol