Influence of some gastrointestinal hormones on adipose tissue lipoprotein lipase activity in vitro: evidence of a stimulatory effect of pancreozymin and gastrin

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

Relationship between lipoprotein lipase activity and plasma sex steroid level in obese women

In obese women (n = 16) at their weight, fasting adipose tissue lipoprotein lipase (LPL) activity, obtained by elution with serum and heparin at 4 degrees and 37 degrees C, was inversely correlated to plasma estradiol levels (r = -0.724; P = 0.002) and (r = -0.641; P = 0.010), respectively. Furthermore, fasting postheparin plasma LPL activity during a heparin infusion, showed an even stronger inverse correlation to plasma estradiol when measured at 60 min (r = -0.815; P less than 0.001). None of the above parameters was correlated to the body mass index. Postprandial LPL activity in postheparin plasma, measured 10 min after a heparin injection, showed a strong positive correlation with plasma free testosterone (r = 0.780; P = 0.001). Neither of these parameters was correlated with the body mass index. The origin of this LPL activity is presently unknown but could conceivably represent a pool of LPL from skeletal muscle. Since it has been shown convincingly that estrogen decreases adipose tissue LPL activity in the rat, the present studies strongly suggest that estradiol is a major negative regulator of fasting adipose tissue LPL activity in women.

Are the metabolic characteristics of congenital intraspinal lipoma cells identical to, or different from normal adipocytes?

Congenital intraspinal lipomas are frequently responsible for progressive neurological deficits caused by distortion or compression of the nervous system. Since fat metabolism in these lesions has not been previously studied, the aim of this study was to determine whether intraspinal lipoma cells behave like lipomas or like normal adipocytes. In 11 patients, intraspinal lipoma cells were compared with normal adipocytes isolated from adjacent subcutaneous adipose tissue for the following parameters: lipoprotein lipase (LPL), lipogenesis from U14C glucose, beta-receptor number, adenylate cyclase activity, cyclic AMP production, and lipolysis in response to beta- and alpha 2-adrenergic agonists. No significant difference between these two cell populations was found, suggesting that intraspinal lipomas are not lipomatous tumors, but hamartomatous lesions capable of growth and regression along with the changes in the rest of the fatty pool. This emphasizes the danger of an abnormal weight gain, as well as the possible usefulness of an hypocaloric diet in patients who worsen in spite of previous surgery.

Stimulatory effects of adenosine, adenosine analogs and insulin on adipose tissue lipoprotein lipase activity and their prevention by phosphodiesterase inhibitors

Adenosine and its 'Ri'- and 'P'-site analogs, N6-phenylisopropyladenosine and 2'-deoxyadenosine, stimulate, like insulin, lipoprotein lipase (LPL) activity in adipose tissue, an effect which is suppressed by cycloheximide. However, adenosine and its analogs do not potentiate the effects of submaximal insulin concentrations. As addition of cyclic AMP phosphodiesterase inhibitors abolishes the LPL stimulatory effects of insulin, adenosine and its analogs, this study suggests that these LPL effects are mediated through common mechanisms which are likely a decrease in cyclic AMP and an increase in LPL biosynthesis.

The effect of parenteral and enteral nutrition on portal and systemic immunoreactivities of gastrin, glucagon and vasoactive intestinal polypeptide (VIP)

To compare the effect of parenteral with enteral nutrition on gastroentero-pancreatic hormones, hypercaloric and hypocaloric nutrient preparations, commonly used clinically, were administered to rats either through cannulae in the jugular vein or gastrostomies. Control rats were fed orally ad libitum. Portal and aortic plasma was collected for radioimmunoassay with antibodies to C-terminal regions of gastrin and glucagon and to N-terminal-to-central regions of glucagon and VIP. Levels of all immunoreactivities were significantly lower in aortic than portal plasma. Apparent clearance of glucagon and gastrin by liver or lung both was enhanced by administration of the hypercaloric nutrient intravenously. Only intragastric hypercaloric nutrition maintained levels of VIP immunoreactivity close to those of control rats. Intragastric administration of either preparation appeared to maintain adequate levels of gastrin. Differences in the levels of glucagon immunoreactivities may be related to the stimulatory effects of metabolites in the lower gut and pancreas.

Hormonal mediation of rat heart lipoprotein lipase activity after fat feeding

The effect of acute fat feeding on the response of two fractions of lipoprotein lipase in heart was explored. In rats, previously fasted, lipoprotein lipase activity released into the perfusate by heparin increased approximately 50% 4 h after fat feeding. The lipase activity remaining in the heart tissue after heparin perfusion showed no significant difference. When rats maintained ad libitum were intubated with glucose 2 h before the fat dose, a relatively larger increase (5-10-fold) in the heparin-releasable lipase activity was observed. The capacity of these hearts to hydrolyze 14C-labeled chylomicrons was also increased 4-5-fold over the controls. Fat ingestion has been reported to elevated plasma corticosteroid levels in rats. When adrenalectomized rats were fed fat, no significant changes in the heparin-releasable lipase activity were observed Hydrocortisone and corticotropin treatment increased the heparin-releasable lipase activity to the same degree as observed with fat feeding. These data suggest that the increase in heart lipoprotein lipase activity following fat feeding is mediated via corticosteroids.