Diurnal Changes in Serum Metabolites and Hormones in Lean and Obese Zucker Rats

Abstract

A study of diurnal patterns of serum hormone levels was made in genetically lean and obese Zucker rats. Serum glucose and insulin were elevated in the obese through the 24-hour period; immunoreactive insulin being 12 times higher in the obese rat. A similar pattern of serum hormone levels in lean and obese rats was found for triiodothyronine, thyroid stimulating hormone and prolactin. At peak levels, prolactin was 2.5 times higher in lean than obese rats (P is less than .01). Thyroxine levels tended to be lower in the obese rats throughout the sampling periods when compared to lean rats. Growth hormone levels were severely depressed in the obese rat with the largest differences between lean and obese rats being observed during the light periods of the cycle. These differences in growth hormone secretion may be responsible for the impaired nitrogen retention in the obese rat. Serum levels of corticosterone were highest at the beginning of the dark cycle and decreased drastically thereafter in the lean rats. The obese rat did not exhibit a distinct pattern of corticosterone secretion and tended to be elevated throughout the periods tested.

Lithium Delays Biochemical Circadian Rhythms in Rats

“…The answer to this problem most likely lies not in the stress of the sacrifice procedure, but rather in the age of the animals used. The form of the corticosterone rhythm has been shown to vary greatly with age [Martin et al, 1978]. The lack of any significant difference in liver glycogen, pineal serotonin, and cere bellar magnesium and cerebellar calcium be tween those animals sacrificed by pentobar bital and those killed by CCF inhalation also argues against any significant influence of the sacrifice procedure in the observed results.…”

“…Pentobarbital was deemed preferable to decapitation for the following reasons: (1) the technique provided a greater volume of blood with less contamination by other tis sues: (2) 1.540 0 .1 0 < 3.558 p < 0.01 (11,97) p < 0.20 (11,97) cycle, and (3) we regarded this procedure as more humane. The plasma corticosterone values (an indicator of stress) found in the control animals were well within values re ported by other investigators using other methods of sacrifice, including decapitation [Kreiger, 1972;Martin et al, 1978;Bahnent et al. 1977], It was puzzling that the expected significant cosinor results for control animals in plasma corticosterone was not observed.…”

“…The rhythm in liver gly cogen seems particularly sensitive to this fac tor, having been reported to be linked to the timing of access to protein when the other components of the diet are freely available [Markara and Angelova, 1976;Peret et al, 1973], a restriction which did not affect the rhythm in corticosterone [Peret et al, 1973], The effect of weight differences is much less clear-cut, with some authors reporting no changes in such rhythms as those found in prolactin and corticosterone between lean and obese individuals [Copinschi et al. 1978;Martin et al" 1978] while others report large differences [Epshtein. 1977], Rhythms of liver lipogcncsis and sensitivity to glucagon have been reported to be quite different be tween obese and lean Zucker rats [.…”

Hypothalamic Neurochemistry and Feeding Behavioral Responses to Clonidine, an Alpha-2-Agonist, and to Trifluoromethylphenylpiperazine, a Putative 5-Hydroxytryptamine-1B Agonist, in Genetically Obese Zucker Rats

“…Clonidine-induced food intake is en hanced during periods of increased plasma corticosterone lev els [31]. Since obese Zueker rats have elevated daytime plasma corticosterone levels [35], the greater response to clonidinestimulated food intake in obese animals could also be medi ated by a higher sensitivity of « 2-adrenoceptors, especially since corticosterone has been shown to upregulate « 2-recep tors within the PVN [36]. Corticosterone may also control feeding behavior by other mechanisms, e.g.…”

A radioimmunoassay of chicken growth hormone using growth hormone produced by recombinant DNA technology : validation and observations of plasma hormone variations in genetically fat and lean chickens

“…This last aspect has to be more thoroughly investigated. It has been observed that mammal obesities are frequently accompanied by abnormally depressed plasma GH concentrations (Sinha et al, 1975 ;Martin et al, 1978 ;Finkelstein et al, 1986 …”