British Journal of'Obstetrics and Gynaerology March 1976. Vol83. pp 241-244
EFFECT OF INSULIN ON ADIPOSE TISSUE LIPOLYSIS IN HUMAN PREGNANCY BY
T. M. COLTART AND
CHRISTINE WILLIAMS Department of Obstetrics and Gynaecology Gu-v's Hospital Medical School, London SEl 9RT Summary Adipose tissue has been shown to retain its sensitivity to the antilipolytic effects of insulin during late pregnancy. This suggests that during late pregnancy, increased adipose tissue lipolysis is due to a lipolytic factor rather than insulin resistance.
INthe fasting state, triglyceride breakdown within adipose tissue (lipolysis) results in a net release of fatty acids into the circulation. During late pregnancy, levels of free fatty acids (FFA) in fasting plasma rise (Burt, 1960; Spellacy and Goetz, 1963; Fairweather, 1971) suggesting that adipose tissue lipolysis is increased, and recent work has shown this to be so (Elliott, 1975). Also in late pregnancy there is impaired glucose tolerance (O'Sullivan, 1970), decreased glucose responsiveness to injected insulin (Burt and Davidson, 1974) and an exaggerated insulin response to a glucose load (Spellacy, 1971) indicating resistance to the normal hypoglycaemic effect of insulin. In addition to its hypoglycaemic role, insulin is known to be antilipolytic (Butcher et al, 1966; Kono and Barham, 1973; Siddle and Hales, 1974), due possibly to the ability of insulin to lower intracellular levels of adenosine 3'3'monophosphate (cyclic AMP). Whether in pregnancy adipose tissue retains its sensitivity to the antilipolytic effect of insulin is uncertain and evidence on this point is conflicting. Burt et al (1962) using insulin and Kalkhoff et al (1964) using tolbutamide, found the same percentage fall in plasma FFA in pregnant and non-pregnant subjects, suggesting that during pregnancy, adipose tissue sensitivity to insulin is retained. The results of in vitro studies on pregnant rat adipose tissue supported this view
(Leake and Burt, 1966; Knopp et al, 1970). On the other hand, Bleicher et al (1964), Quinto et al (1967) and Sabata et a1 (1968) all found diminished plasma FFA response to insulin during pregnancy, suggesting resistance to insulin within adipose tissue. We decided to investigate the direct effect of insulin on adipose tissue lipolysis of human subjects during early and late pregnancy. AND METHODS PATIENTS Adipose tissue was obtained from the anterior abdominal wall of patients undergoing elective Caesarean section, termination of pregnancy and gynaecological surgery. The respective mean age of the patients from each group was 32, 24 and 35 years. None of the patients was grossly overweight, and in the control group, none was taking oral contraceptives or receiving hormone therapy. The tissue was transferred to the laboratory in a thermos flask containing buffer at 37 "C. Pieces of tissue weighing approximately 200 mg were cut and placed in glass stoppered test tubes containing incubation media at 37 "C. The tissue was pre-incubated for 30 minutes at 37 "C in a shaking water bath, the gas phase being O,:CO,, 95 : 5. The incubation medium consisted of 1 ml of Earl's bicarbonate buffer pH 7.5 containing 1 per cent bovine plasma albumin. The buffer was gassed for 30 minutes before use. After
241
242 COLTART AND
WILLIAMS
half-an-hour, the tissue was removed, blotted and placed into 1 ml of fresh medium. Isoprenaline ( 10-5M) and bovine insulin (10T8M) were added at this stage in 50 p1 volumes. The test tubes were gassed and the incubation continued for one hour. At the end of the incubation the tissues were removed, blotted and weighed and the incubation media stored at -4 "C for glycerol determination. Lipolysis was calculated from the glycerol released into the medium during the incubation period and expressed as nmoles of glycerol released per mg of adipose tissue per hour. Glycerol was assayed using a semi-automated enzymatic procedure based on the method of Eggstein and Kreutz (1966).
RESULTS Basal lipolysis was significantly higher in late pregnancy adipose tissue (0 112SO -002 nmoles/
-
0.8
0.7
Late Pregnancy (12)
0Non Pregnant (12)
0.6
a
Early Pregnancy(61
-
f
\
0.5 . P v1 )
0
E
0.4 --
e
U 0,
30.3
0
0.2
0.1
0
h Basal
m
Isoprenaline Isoprenaline t
Insulin
FIG.1 Adipose tissue lipolysis. Bars indicate standard errors of the mean.
mg/hour; Mean+SE) than in either early pregnancy tissue (0.083 &0.005 nmoles/mg/ hour; P
EFFECT OF INSULIN ON ADIPOSE TISSUE LIPOLYSIS IN HUMAN PREGNANCY BY
T. M. COLTART AND
CHRISTINE WILLIAMS Department of Obstetrics and Gynaecology Gu-v's Hospital Medical School, London SEl 9RT Summary Adipose tissue has been shown to retain its sensitivity to the antilipolytic effects of insulin during late pregnancy. This suggests that during late pregnancy, increased adipose tissue lipolysis is due to a lipolytic factor rather than insulin resistance.
INthe fasting state, triglyceride breakdown within adipose tissue (lipolysis) results in a net release of fatty acids into the circulation. During late pregnancy, levels of free fatty acids (FFA) in fasting plasma rise (Burt, 1960; Spellacy and Goetz, 1963; Fairweather, 1971) suggesting that adipose tissue lipolysis is increased, and recent work has shown this to be so (Elliott, 1975). Also in late pregnancy there is impaired glucose tolerance (O'Sullivan, 1970), decreased glucose responsiveness to injected insulin (Burt and Davidson, 1974) and an exaggerated insulin response to a glucose load (Spellacy, 1971) indicating resistance to the normal hypoglycaemic effect of insulin. In addition to its hypoglycaemic role, insulin is known to be antilipolytic (Butcher et al, 1966; Kono and Barham, 1973; Siddle and Hales, 1974), due possibly to the ability of insulin to lower intracellular levels of adenosine 3'3'monophosphate (cyclic AMP). Whether in pregnancy adipose tissue retains its sensitivity to the antilipolytic effect of insulin is uncertain and evidence on this point is conflicting. Burt et al (1962) using insulin and Kalkhoff et al (1964) using tolbutamide, found the same percentage fall in plasma FFA in pregnant and non-pregnant subjects, suggesting that during pregnancy, adipose tissue sensitivity to insulin is retained. The results of in vitro studies on pregnant rat adipose tissue supported this view
(Leake and Burt, 1966; Knopp et al, 1970). On the other hand, Bleicher et al (1964), Quinto et al (1967) and Sabata et a1 (1968) all found diminished plasma FFA response to insulin during pregnancy, suggesting resistance to insulin within adipose tissue. We decided to investigate the direct effect of insulin on adipose tissue lipolysis of human subjects during early and late pregnancy. AND METHODS PATIENTS Adipose tissue was obtained from the anterior abdominal wall of patients undergoing elective Caesarean section, termination of pregnancy and gynaecological surgery. The respective mean age of the patients from each group was 32, 24 and 35 years. None of the patients was grossly overweight, and in the control group, none was taking oral contraceptives or receiving hormone therapy. The tissue was transferred to the laboratory in a thermos flask containing buffer at 37 "C. Pieces of tissue weighing approximately 200 mg were cut and placed in glass stoppered test tubes containing incubation media at 37 "C. The tissue was pre-incubated for 30 minutes at 37 "C in a shaking water bath, the gas phase being O,:CO,, 95 : 5. The incubation medium consisted of 1 ml of Earl's bicarbonate buffer pH 7.5 containing 1 per cent bovine plasma albumin. The buffer was gassed for 30 minutes before use. After
241
242 COLTART AND
WILLIAMS
half-an-hour, the tissue was removed, blotted and placed into 1 ml of fresh medium. Isoprenaline ( 10-5M) and bovine insulin (10T8M) were added at this stage in 50 p1 volumes. The test tubes were gassed and the incubation continued for one hour. At the end of the incubation the tissues were removed, blotted and weighed and the incubation media stored at -4 "C for glycerol determination. Lipolysis was calculated from the glycerol released into the medium during the incubation period and expressed as nmoles of glycerol released per mg of adipose tissue per hour. Glycerol was assayed using a semi-automated enzymatic procedure based on the method of Eggstein and Kreutz (1966).
RESULTS Basal lipolysis was significantly higher in late pregnancy adipose tissue (0 112SO -002 nmoles/
-
0.8
0.7
Late Pregnancy (12)
0Non Pregnant (12)
0.6
a
Early Pregnancy(61
-
f
\
0.5 . P v1 )
0
E
0.4 --
e
U 0,
30.3
0
0.2
0.1
0
h Basal
m
Isoprenaline Isoprenaline t
Insulin
FIG.1 Adipose tissue lipolysis. Bars indicate standard errors of the mean.
mg/hour; Mean+SE) than in either early pregnancy tissue (0.083 &0.005 nmoles/mg/ hour; P
