The Response of Cyclic Nucleotide Content in Liver and Brown Fat of Rats Weaned to Different Diets

Abstract

Rats were weaned on the 18th or 30th postnatal day to a high-fat, high-carbohydrate or atherogenic diet. Twenty-four hours later, hepatic levels of cyclic guanosine 3',5'-monophosphate (cyclic GMP) and adenosine, 3',5'-cyclic monophosphate (cyclic AMP) were found to be higher in male animals aged 31 days fed the high-fat than those fed the high-carbohydrate diet. Prematurely weaned rats (day 18) reacted in the same way. However, feeding either diet resulted in higher hepatic cyclic nucleotide levels than found in rats kept with the dam. The atherogenic diet was least effective in raising these levels. After a 24-hour fast, cyclic nucleotide levels in liver and brown fat were elevated and hepatic levels could not be lowered by 6 hours of feeding the high-fat or atherogenic diet. In male 40-day-old rats, however, feeding for 2 hours was sufficient to lower these levels, more so with a high-carbohydrate than a high-fat diet. Since blood levels of glucagon are high, and those of insulin are low in 18-day-old rats that are not weaned and since their hepatic cyclic nucleotide levels are low, it is suggested that other factors, in addition to blood hormone levels, play a role in regulating cyclic nucleotide levels.

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“…Theoretically, the incretin effect of GLP-1, as well as ghrelin, would have an anabolic effect on metabolism [325,385], whereas higher circulating levels of PYY increase fatty acid oxidation and decrease energy efficiency [375]. A diet high in protein at the expense of carbohydrate would furthermore translate into a higher glucagon:insulin ratio, known to increase intracellular levels of cAMP in both liver and adipose tissue [408][409][410][411]. SREBPs/LXR↑↑ SREBPs/LXR↑ [189,190] ChREBP↑↑ ChREBP↑ [197] Fructose Unclear Increased Unclear [67,68] Fatty acids Saturated fatty acids Stimulation Increased [24,180,[399][400][401][402][403][404] All PPARs↑ [121][122][123][124]180] n-3 PUFAs Inhibition Decreased [23,29,137,[420][421][422][423][424][425][426] PPARα↑↑↑ PPARα↑↑↑ [121,124,130,180] PPARγ↓ PPARγ↓ [166][167][168][169]180] SREBPs/LXR↓↓ SREBPs/LXR↓↓ …”