Dose-response effects of free fatty acids on glucose and lipid metabolism during somatostatin blockade of growth hormone and insulin in humans.
BACKGROUND
GH and other stress hormones stimulate lipolysis, which may result in free fatty acid (FFA)-mediated insulin resistance. However, there are also indications that FFAs in the very low physiological range have the same effect.


OBJECTIVE
The objective of the study was to address systematically the dose-response relations between FFAs and insulin sensitivity.


METHODS
We therefore examined eight healthy men for 8 h (6 h basal and 2 h glucose clamp) on four occasions.


METHODS
Intralipid was infused at varying rates (0, 3, 6, 12 microl.kg(-1).min(-1)); lipolysis was blocked by acipimox; and endogenous GH, insulin, and glucagon secretion was blocked by somatostatin and subsequently replaced at fixed rates.


RESULTS
This resulted in four different FFA levels between 50 and 2000 micromol/liter, with comparable levels of insulin and counterregulatory hormones. Both in the basal state and during insulin stimulation, we saw progressively decreased glucose disposal, nonoxidative glucose disposal, and forearm muscle glucose uptake at FFA levels above 500 micromol/liter. Apart from forearm glucose uptake, the very same parameters were decreased at low FFA levels (approximately 50 micromol/liter). FFA rate of disposal was linearly related to the level of FFAs, whereas lipid oxidation reached a maximum at FFA levels approximately 1000 micromol/liter.


CONCLUSIONS
In the presence of comparable levels of all major metabolic hormones, insulin sensitivity peaks at physiological levels of FFAs with a gradual decrease at elevated as well as suppressed FFA concentrations. These data constitute comprehensive dose-response curves for FFAs in the full physiological range from close to zero to above 2000 micromol/liter.
Gormsen
L C
LC
Medical Department M, Aarhus University Hospital, Aarhus University, Nørrebrogade 42, DK-8000 Aarhus C, Denmark. lars.christian.gormsen@ki.au.dk
Jessen
N
N
Gjedsted
J
J
Gjedde
S
S
Nørrelund
H
H
Lund
S
S
Christiansen
J S
JS
Nielsen
S
S
Schmitz
O
O
Møller
N
N
D000328:Adult; D002153:Calorimetry, Indirect; D016207:Cytokines / Q000097:blood; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005542:Forearm / Q000098:blood supply; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique; D019382:Human Growth Hormone / Q000037:antagonists & inhibitors*; D006801:Humans; D007328:Insulin / Q000502:physiology; D007329:Insulin Antagonists; D050356:Lipid Metabolism / Q000187:drug effects*; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D017551:Microdialysis; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D010168:Palmitates / Q000494:pharmacology; D012039:Regional Blood Flow / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013004:Somatostatin / Q000494:pharmacology*
D016207:Cytokines; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007329:Insulin Antagonists; D010168:Palmitates; D019382:Human Growth Hormone; D013004:Somatostatin; D005947:Glucose