Action of growth hormone and thyroxine on aortas of hypophysectomized dogs

Aortic compliance measurements using Doppler ultrasound: in vivo biochemical correlates

A noninvasive Doppler ultrasound technique for the assessment of aortic compliance based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway is described. An approach for correcting for the effect of blood pressure on aortic distensibility is considered. The derivation of an index of intrinsic distensibility, Cp, which is independent of blood pressure, is provided and applied to data collected from normal, healthy volunteers. Overviews are provided of studies utilising the technique to determine aortic compliance in medical disorders, which are known to predispose to premature cardiovascular disease, such as diabetes mellitus, familial hypercholesterolaemia and growth hormone deficiency. The significance of correlations between in vivo aortic compliance measurements and plasma concentrations of total cholesterol, low-density-lipoprotein cholesterol, high-density-lipoprotein cholesterol and insulin-like growth factor-I are discussed. It is proposed that the measurement of aortic compliance in normal, healthy individuals may potentially be a useful in vivo research tool for investigating the effects of biochemical factors on the biophysical properties of the aortic wall. Furthermore, we believe that the routine measurement of blood pressure-corrected aortic distensibility may prove a useful, noninvasive clinical tool for assessing patients' susceptibility to atherosclerosis, as well as for monitoring their response to therapeutic interventions.

Non-invasive Doppler ultrasound technique for the in vivo assessment of aortic compliance

A non-invasive Doppler ultrasound technique for the assessment of aortic compliance is described. This is based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway. A structured protocol has been developed to improve the reproducibility of the technique as well as for the purposes of operator training. Preliminary results of a study of both the intra- and inter-observer variability of the method are provided and problems associated with the technique are discussed. Medical disorders such as atherosclerosis, diabetes mellitus and familial hypercholesterolaemia have all been shown to affect arterial wall compliance. We suggest that the measurement of aortic compliance in vivo may be a useful, non-invasive tool for assessing these patients' susceptibility to atheromatous arterial disease and for monitoring their response to therapy.

Arterial wall compliance in diabetes

A non-invasive Doppler ultrasound technique, based on the measurement of pulse wave velocity along the aorta, has been used to deduce aortic compliance in 25 Type 1 and 25 Type 2 diabetic patients. Thirteen of the Type 1 diabetic group had their compliance measured within 1 year of diabetes first being clinically diagnosed. All compliance values were normalized for age and sex variations using data previously obtained from over 600 normal, non-diabetic subjects (mean normalized compliance +/- SD; 100 +/- 15%). The results show that Type 1 diabetic patients have significantly more distensible aortas (132 +/- 26%) than their age- and sex-matched non-diabetic counterparts (100 +/- 12%) (p less than 0.01), while Type 2 diabetic patients have significantly stiffer aortas (74 +/- 21%) than their age- and sex-matched non-diabetic counterparts (100 +/- 18%) (p less than 0.01). The young Type 1 diabetic patients measured within 1 year of diagnosis have aortas ranging up to 78% more distensible (151 +/- 15%) than their age- and sex-matched non-diabetic controls (100 +/- 11%) (p less than 0.001). These results support findings by other groups that adult diabetic patients have less distensible arteries than normal, but contradict reports in the literature dating back over 20 years that diabetic children have stiffer arteries than normal children.

STZ-induced diabetes in SHR and renovascular hypertensive rats: dissociation between changes in arterial pressure and vascular collagen synthesis

Streptozotocin (STZ)-induced diabetes depresses the rate of vascular collagen synthesis in the spontaneously hypertensive rat (SHR), but it also reduces arterial pressure (SAP) in this strain. We investigated this phenomenon further by comparing the SHR with the renovascular hypertensive (RVH) rat, because diabetes does not affect SAP in the latter model of hypertension. Renovascular hypertension was induced by clipping the left renal artery of Wistar-Kyoto (WKY) rats; sham-operated WKY were included as normotensive controls. Collagen synthesis of arterial tissue in vitro was quantified as prolyl hydroxylase activity and the rate of radioactive proline incorporation into collagen. Arterial collagen synthesis of nondiabetic SHR and RVH animals was elevated compared to that of the nonhypertensive WKY controls. STZ-induced diabetes (8 weeks) reduced SAP of SHR, but had no effect on SAP of either RVH or normotensive WKY rats. However, diabetes significantly depressed vascular collagen synthesis of both SHR and RVH rats, and, less consistently, of the WKY. The results strongly suggest that STZ-induced diabetes in SHR impairs arterial collagen synthesis independent of associated changes in arterial pressure.

The effect of glucagon on the glycosaminoglycan content of canine arteries

Hypophysectomized young beagles were treated for 21 days with pharmacological doses of glucagon, administered intramuscularly in two daily injections of 0.5 mg each. Hyaluronic acid, heparan, dermatan and isomeric chondroitin sulphates were determined in aorta, carotid, iliac, renal, mesenteric and coronary arteries. In comparison with age-matched hypophysectomized controls, glucagon-treated dogs showed a reduction in the heparan sulphate concentration in their carotid arteries and thoracic aorta. These results indicate that glucagon has a very limited effect on arterial glycosaminoglycan content.

The relationship of hormones to arterial glycosaminoglycans and atherosclerosis

Glycosaminoglycan fractions were measured in representative large and medium sized arteries of normal, hypophysectomized and hormone treated young beagles. Hyaluronate, heparan sulphate, dermatan sulphate and the isomeric chondroitin sulphates were determined in the aortic arch, thoracic and abdominal segments, in the external iliac, superior mesenteric, renal, common carotid and coronary arteries. The hormones used for replacement therapy of hypophysectomized animals were growth hormone, thyroxine, cortisone and the sex hormones testosterone, estrogen and progesterone. The sensitivity to an individual hormone was found to differ in various segments of the arterial tree; the thoracic and abdominal aorta were most responsive but renal and superior mesenteric arteries were relatively inert. The hypothesis is advanced that arteries with a GAG metabolism highly sensitive to hormones are more prone to develop atherosclerosis than arteries that have a limited sensitivity to alterations in endocrine balance.

The effect of sex hormones on glycosaminoglycan content of canine aorta and coronary arteries

Hyaluronate (HA), heparan sulfate (HS), dermatan sulfate (DS) and isomeric chondroitin sulfates (CS) were measured in vascular walls of 9-10 months old normal and hypophysectomized female beagles treated with sex hormones. Following hypophysectomy the animals were maintained for 8 weeks without any hormonal replacement therapy and then they were exposed for 3 weeks to parenteral treatment with sex hormones. One group received twice weekly 25 mg testosterone, another group was given the same amount of progesterone, and a third group received on day 1 and day 14, estrogens in 2 injections, consisting of a mixture of 10 mg short-acting estradiol-17-phenylpropionate and 2.5 mg long-acting estradiol benzoate. After 11 weeks all animals were sacrificed, coronary arteries and aortas were immediately removed and the latter were divided into three segments: arch, thoracic and abdominal. Removal of the pituitary led to a reduction of the HA content in the aortic arch and thoracic segment, but coronary arteries and abdominal aorta were not affected. The main consequence of hypophysectomy both in the entire aorta and in coronary arteries was a sharp reduction of the sulfated glycosaminoglycan (GAG) content. All three hormones produced a modest rise in the HS content of coronary arteries. A more definite response was seen in the thoracic aorta where each of the three hormones raised the low DS content to normal levels. Concerning the effect of sex hromones on aortic GAG other than DS, TESTOSTERONE RAISED THE CS content towards normal in thoracic and abdominal segments, while estrogen by doubling the normal HA concentration was particularly potent in the abdominal aorta. It is conceivable that the different sensitivity of various segments of aorta and coronary arteries to sex (and other) hormones in terms of regulating GAG metabolism may prove to be of relevance to the uneven distribution of lesions in degenerative vascular disease.