Experimental dog model for assessment of fasting and postprandial fatty acid metabolism: pitfalls and feasibility

The dog is a widely-used model for conducting metabolic studies. This is mainly due to its large size and its physiology which is relatively similar to that of humans. Here, we attempted to optimize a postprandial metabolic study protocol used in dogs. Following acclimatization, female mongrel dogs underwent 9 h profiling for time-course baseline plasma data on triglyceride, adrenocorticotropic hormone (ACTH) and cortisol levels. One week later, carotid and jugular catheters were surgically inserted for sampling and infusions. Initial post-operative care, based on the literature (Protocol 1), consisted of analgesia (buprenorphine every 8-12 h and 2-3 doses/day of acepromazine), restriction by Pavlov harness within cages, and a two- to three-day recovery period. Throughout the experiment, dogs received a lipid tracer diluted in 5% bovine serum albumin (BSA). Compared with baseline, animals vomited (n = 6/6) and exhibited high ACTH + cortisol levels (stress biomarkers), resulting in blunted triglyceride peak levels. To avoid these undesirable effects, post-operative care was modified (Protocol 2) as follows: animals (n = 19) were given a single dose of buprenorphine and no acepromazine, were unrestrained and free to move within cages, the recovery period was extended to seven days, and the lipid tracer was diluted in 0.002% versus 5% BSA. Using this modified protocol, postprandial plasma-triglyceride and ACTH/cortisol patterns were similar to baseline values. Controlling for stressors, as well as for factors which may alter proper digestion, is critical for all postprandial metabolic studies. Our results show that an optimized postprandial metabolic protocol used in dogs reduces experimental variability, while improving animal care and comfort.

Lasting alterations of the sodium current by short-term hyperlipidemia as a mechanism for initiation of cardiac remodeling

Clinical and animal studies indicate that increased fatty acid delivery to lean tissues induces cardiac electrical remodeling and alterations of cellular calcium homeostasis. Since this may represent a mechanism initiating cardiac dysfunction during establishment of insulin resistance and diabetes or anaerobic cardiac metabolism (ischemia), we sought to determine if short-term exposure to high plasma concentration of fatty acid in vivo was sufficient to alter the cardiac sodium current ( INa) in dog ventricular myocytes. Our results show that delivery of triglycerides and nonesterified fatty acids by infusion of Intralipid + heparin (IH) for 8 h increased the amplitude of INa by 43% and shifted its activation threshold by −5 mV, closer to the resting membrane potential. Steady-state inactivation (availability) of the channels was reduced by IH with no changes in recovery from inactivation. As a consequence, INa “window” current, a strong determinant of intracellular Na+ and Ca2+ concentrations, was significantly increased. The results indicate that increased circulating fatty acids alter INa gating in manners consistent with an increased cardiac excitability and augmentation of intracellular calcium. Moreover, these changes could still be measured after the dogs were left to recover for 12 h after IH perfusion, suggesting lasting changes in INa. Our results indicate that fatty acids rapidly induce cardiac remodeling and suggest that this process may be involved in the development of cardiac dysfunctions associated to insulin resistance and diabetes.

Are the annual reproductive and body weight rhythms in the male European hamster (Cricetus cricetus) dependent upon a photoperiodically entrained circannual clock?

Most of the data obtained so far on the European hamster (Cricetus cricetus) suggest direct photoperiodically driven seasonal changes in sexual activity and body weight. The results of the present long-term study support the hypothesis that these annual changes are the expression of photoperiodically driven endogenous circannual rhythms. When subjected following capture (April-May) to constant conditions of long photoperiod (LP) and constant temperature a large number of the European hamsters present, in September-December, complete gonadal atrophy associated with a decrease in body weight. A sexual reactivation as well as an increase in body weight are observed in the same animals between January and April. Of the six animals that survived long enough, two only presented partial gonadal atrophy during the second year. These observations clearly demonstrate that the decline in sexual activity in subjective autumn does not require a decrease in photoperiod, at least in the first year. Theoretically, the observed rhythms, if circannual in nature, would be generated by a self-sustained annual oscillator (circannual clock) able to function in the absence of a photoperiodic input. Pinealectomy makes animals unable to detect or measure photoperiodic information. Of the six European hamsters tested (pinealectomized in June and then kept continuously under LP), five showed clear annual rhythms in body weight and reproductive capacities for two consecutive years. Clearly endogenous annual rhythms were expressed in these conditions. To be entrained to a 1-year period, such a circannual clock should, however, be able to react to either LP and/or to short-photoperiod (SP), at least at certain periods of the annual cycle. In animals exposed to LP in August or October, after gonadal atrophy had been established by exposure to natural SP, gonadal regrowth started in December or January, about 2 to 3 months earlier than in animals kept outside or in experimental SP. With the same experimental conditions, exactly the same results were obtained in pinealectomized animals; thus stimulatory effect of LP or LP-induced phase advance of the circannual clock can be excluded. The absence of the SP information would then induce such reaction. In animals kept under constant LP and temperature following capture, however, pinealectomy in January--when all animals are sexually active--induces gonadal atrophy within--weeks. This clearly demonstrates that LP is stimulatory at this time of the subjective year.