Factors influencing the lipolytic response of swine (Sus domesticus) adipose tissue: ontogeny

Is the lipolytic response in porcine adipose tissue slices equivalent to the lipolytic response in isolated adipocytes?

1. In most cases, when isolated adipocytes and adipose tissue slices from the same animal were stimulated with various lipolytic agents (adrenergic agonists, theophylline, adenosine deaminase), the qualitative response was similar. 2. There were, however, numerous exceptions; e.g. quinterenol did not affect isolated adipocytes whereas it was a partial agonist for adipose slices from the same animal. 3. The adipocytes present in slices were larger than those isolated from slices by collagenase digestion. 4. Isolated adipocytes were not more sensitive than tissue slices to stimulation by lipolytic agents.

Adenosine-theophylline interactions on the lipolytic response to beta-adrenergic agonists in porcine adipose tissue

1. Many beta-adrenergic agonists did not stimulate porcine adipose tissue slice lipolysis unless theophylline, an antagonist of the adenosine receptor was added to the incubation medium. 2. In contrast to previous results, theophylline itself was an effective lipolytic agonist in tissue from many pigs. 3. Lipolysis was partially inhibited by adenosine or phenylisopropyl adenosine. Lipolysis was marginally stimulated by adenosine deaminase or 8-phenyltheophylline. 4. The data suggest that the mechanism of theophylline stimulation of lipolysis was only partially through antagonism of the adenosine receptor.

Acute effects of metabolic hormones in swine

Many metabolic hormones (glucagon, hydrocortisone, corticosterone, TSH, thyroxine and triiodothyronine) did not stimulate porcine adipose tissue lipolysis in vitro. Growth hormone and ACTH stimulated lipolysis at high concentrations, in the presence of theophylline. Insulin inhibited lipolysis. Infusion of metabolic hormones with measurement of plasma free fatty acid and glycerol concentrations, purportedly indicative of in vivo lipolysis, indicated that glucagon and somatotropin had no effect, adrenocorticotropin increased and insulin depressed plasma concentrations of the metabolites. Overall, the in vitro predicts the in vivo response. There were exceptions, e.g. adrenocorticotropin moderately increased plasma metabolites but had little effect in vitro.