Ambulatory 24-hour blood pressure monitoring: correlation between blood pressure variability and left ventricular hypertrophy in untreated hypertensive patients

BACKGROUND

Left ventricular hypertrophy (LVH) appears to be poorly correlated with clinical measurements of blood pressure: a better correlation may be observed with data from 24 h ambulatory blood pressure monitoring (ABPM). The aim of this study was to compare the results of non-invasive ABPM in a population of patients with essential hypertension who had never been treated, subdividing them based on the presence or absence of LVH in the transthoracic echocardiogram (LVMI, left ventricular mass index > 135 g/m2 in males and > 110 g/m2 in females).

METHODS

Eighty hypertensive patients with mild or moderate hypertension underwent routine blood tests, a 24 h ABPM and a transthoracic echocardiogram. Based on the ABPMs, we analyzed average 24 h systolic and diastolic blood pressure (BP), average daytime (6 a.m.-10 p.m.) and nighttime (10 p.m.-6 a.m.) systolic and diastolic BP, average morning (6-12 a.m.) BP and the number of dipper or non-dipper patients. The echocardiographic study included the calculation of left ventricular mass using Devereux's formula according to the Penn convention, analysis of the patterns of left ventricular geometry and a study of left ventricular diastolic function.

RESULTS

Thirty-five (43.7%) patients had LVH at the echocardiographic study. In 52 subjects, the clinical history showed at least one BP measurement > 140/90 mmHg in the year prior to our observation. The average age was 48 +/- 11, without any significant correlation to LVMI (r = 0.13). The magnitude of the S-wave in V1 and the R-wave in V5 and the magnitude of the tallest R-wave and S-wave in the electrocardiogram analysis had a significant correlation with LVMI (r = 0.23 and r = 0.26, respectively). The echocardiogram revealed a normal left ventricular geometry in 43.8% of hypertensive patients, concentric remodeling in 13.8%, concentric hypertrophy in 16.2% and eccentric hypertrophy in 26.2%. The isovolumic relaxation time (IVRT) and A-wave were significantly correlated with LVMI (r = 0.49 and r = 0.33, respectively). LVMI had a significant correlation with systolic BP at ABPM (24 h systolic BP r = 0.34; daytime systolic BP r = 0.35; nighttime systolic BP r = 0.28; 6-12 systolic BP r = 0.29) but not with diastolic BP. Dipper patients represented 76.3% of the population, without any difference in LVMI between dippers and non-dippers (p = 0.09). Dipper patients had a higher prevalence of normal left ventricles as compared with non-dippers (p < 0.0001). White-coat hypertension was observed in 7.5% of hypertensive patients.

CONCLUSIONS

The prevalence of LVH in our population was high (43.7%) and some parameters related to diastolic left ventricular function (IVRT, A-wave) were correlated with LVMI. Systolic ambulatory BP was significantly correlated with LVMI, while diastolic BP was not.

Effects of cholinergic blockade by pirenzepine on insulin and glucose response to oral and intravenous glucose and to arginine load in obesity

Parasympathetic nervous system is known to affect insulin secretion in animal and man and there is evidence that it is involved in the outcome of spontaneous and stimulated insulin hypersecretion observed in animal obesity. In human obesity, there are contradictory data. We studied the effect of 150 mg orally administered pirenzepine (PNZ), a muscarinic receptor antagonist, on the insulin response to glucose (75 g p.o. or 0.33 g/kg i.b.w. i.v.) or arginine (0.5 g/kg infused in 30 min) in 18 obese subjects normotolerant to glucose. PNZ did not modify basal serum insulin and the hormone response to either intravenous glucose (AUC: 5221.6 +/- 1177:6 vs 5309.8 +/- 1534.8 mU/L.min) or arginine load (4257.9 +/- 832.7 vs 3952.8 +/- 549.3 mU/L.min). Calculated as AUC the insulin response to oral glucose load was unaffected by PNZ (6601.5 +/- 1218.6 vs 8614.3 +/- 1095.2 mU/L.min). Actually, the insulin rises at +30 min after oral glucose load was significantly blunted by PNZ (37.0 +/- 3.4 vs 81.6 +/- 16.9 mU/L; p < 0.03). However, after statistical evaluation by ANCOVA assuming basal insulin and +30 min glucose levels as covariates, this significant disappeared. Our present data do not agree with the hypothesis that the cholinergic system plays a role in the exaggerated insulin secretion of obesity. Nevertheless, these findings confirm that acetylcholine positively influences insulin secretion in humans, likely via indirect mechanisms.

Effects of acipimox, an antilipolytic drug, on the growth hormone (GH) response to GH-releasing hormone alone or combined with arginine in obesity

Increased free fatty acid (FFA) levels of obese patients are likely involved in the pathogenesis of the growth hormone (GH) hyposecretion of obesity. To clarify their role, we studied the influence of inhibition of plasma FFA levels, induced by 500 mg oral acipimox (ACX), an antilipolytic drug, on the GH response to GH-releasing hormone (GHRH) alone or combined with arginine ([ARG] study A) in six normal women ([NS] aged 24 to 37 years; body mass index, 22.4 +/- 0.9 kg/m2) and six obese women ([OB] aged 21 to 40 years; body mass index 39.5 +/- 3.2 kg/m2). In a group of seven OB patients (aged 18 to 58 years; body mass index, 35.8 +/- 1.3 kg/m2), the effect of ACX on either GHRH- or GHRH+ARG-stimulated GH increase was also studied after a 4-day treatment with the same drug at 250 mg three times daily (study B). OB patients had baseline FFA levels higher than NS (0.77 +/- 0.06 v 0.44 +/- 0.09 mmol/L, P<.05). In study A, ACX reduced FFA levels to the same nadir in both groups (0.11 +/- 0.02 and 0.12 +/- 0.03 mmol/L, NS and OB subjects, respectively). In NS, ACX failed to significantly potentiate the GH response to either GHRH (1,371.9 +/- 425.2 v 1,001.8 +/- 229.0 micrograms/L x min) or GHRH+ARG (3558.4 +/- 1,513.7 v 3,045.9 +/- 441.8 micrograms/L x min), while in OB patients it increased the GH response to GHRH (797.6 +/- 277.3 v 353.8 +/- 136.7 micrograms/L x min, P<.01) and did not modify the response to ARG+GHRH (1,010.5 +/- 253.1 v 821.1 +/- 222.0 micrograms/L x min). In study B, ACX reduced FFA levels in OB patients (nadir, 0.09 +/- 0.04 mmol/L). This treatment strikingly increased the GH response to GHRH (1,734.0 +/- 725.4 v 271.5 +/- 112.8 micrograms/L x min, P<.01) and significantly potentiated that to ARG+GHRH (2,371.9 +/- 571.3 v 1,020.0 +/- 343.2 micrograms/L x min, P<.05). In conclusion, our present findings indicate that an acute reduction of plasma FFA levels in OB patients restores their somatotrope responsiveness, whereas it does not affect GH secretion in lean subjects. After prolonged treatment, ACX further improves GHRH-stimulated GH secretion in OB patients, suggesting that elevated FFA levels play a leading role in the GH hyposecretory state of obesity.

Short-term fasting in obesity fails to restore the blunted GH responsiveness to GH-releasing hormone alone or combined with arginine

OBJECTIVE

Fasting is known to clearly increase both spontaneous and GHRH-stimulated GH secretion in normal subjects and this effect is likely to be due to hypothalamic mechanism(s). Our aim was to clarify the effect of a 3 or 4-day fast, on the GH response to GHRH alone or combined with arginine, an amino acid probably acting via inhibition of hypothalamic somatostatin release.

DESIGN

Two tests with GHRH (1 microgram/kg i.v.), administered either alone or in combination with arginine (ARG, 0.5 g/kg i.v.) were performed, in a randomized order at least 3 days apart. In obese women the two tests were repeated after a 3 or 4-day fast.

PATIENTS

Seven obese women (OB, aged 17-54 years, BMI 42.4 +/- 3.6 kg/m2, waist-hip ratio (WHR) 0.85 +/- 0.01) and ten healthy women, as control subjects (CS, aged 20-44 years, BMI 23.1 +/- 1.1 kg/m2, WHR 0.79 +/- 0.01) were studied.

MEASUREMENTS

Serum GH and IGF-I levels were measured by radioimmunoassay. The GH secretory responses were expressed either as absolute values (mU/l) or as areas under the curve (AUC, mU/l/h) calculated by trapezoidal integration. IGF-I concentrations were expressed as absolute values (microgram/l) with reference to a pure recombinant IGF-I preparation. Results are expressed as mean +/- SEM.

RESULTS

Basal GH and IGF-I levels in OB were lower than in CS (0.8 +/- 0.2 vs 4.8 +/- 1.0 mU/l, P < 0.0001 and 120.1 +/- 21.4 vs 188.7 +/- 13.1 micrograms/l, P < 0.02, respectively). The GHRH-induced GH rise in OB was lower (P < 0.00001) than in CS (AUC 340.2 +/- 81.0 vs 2125.0 +/- 199.6 mU/l/h). ARG increased the GHRH-induced GH rise in both groups, but in OB the GH response to ARG+GHRH (1458.4 +/- 439.0 mU/l/h, P < 0.03 vs GHRH alone) remained lower (P < 0.0001) than in CS (6396.2 +/- 772.2 mU/l/h, P < 0.01 vs GHRH alone). In spite of a reduction in body weight and IGF-I, insulin and glucose levels, in OB fasting failed to modify both the basal GH levels and the somatotroph responsiveness to GHRH when administered either alone or combined with ARG. An increase in free fatty acids (FFA) was also found after fasting.

CONCLUSIONS

The results of this study demonstrate that in obesity the somatotroph hyporesponsiveness to GHRH, either alone or combined with arginine, is not improved by short-term fasting. As fasting is considered a CNS mediated stimulus to GH secretion, its ineffectiveness in obesity does not support a hypothalamic pathogenesis and suggests that long standing metabolic alterations, such as hyperinsulinaemia and/or elevated free fatty acids, could play a major role in causing GH insufficiency in obese patients.

Arginine enhances the growth hormone-releasing activity of a synthetic hexapeptide (GHRP-6) in elderly but not in young subjects after oral administration

In man the GH-releasing hexapeptide His-DTrp-Ala-Trp-DPhe-Lys-NH2 (GHRP-6) has been shown to be active even after oral administration. On the other hand, it has been shown that arginine (ARG) totally restores the reduced somatotropic responsiveness to GHRH observed in aging. Based on the foregoing, in this study we verified the GH-releasing activity of oral GHRP-6 (300 micrograms/kg) in normal aging and the possible enhancing effect of 8 g oral ARG on the GH-releasing effect of GHRP-6. Eight young (age 24-32 yr) and 8 elderly (age 66-85 yr) subjects were studied. In all the GH response to GHRH (1 microgram/kg iv) was also studied. Both IGF-I levels and the GH response to iv GHRH were lower in elderly than in young subjects (mean +/- SE, IGF-I: 65.1 +/- 9.1 vs 142.9 +/- 9.4 micrograms/L, p < 0.0001; GH peak: 5.4 +/- 1.0 vs 13.6 +/- 0.8 micrograms/L, p < 0.0001). Oral GHRP-6 administration induced a GH rise in elderly which was lower, though not significantly, than that in young subjects (GH peak: 9.9 +/- 2.0 vs 16.2 +/- 5.4 micrograms/L). Oral ARG administration enhanced the GHRP-6-induced GH rise in elderly (GH peak: 22.1 +/- 3.3 micrograms/L, p < 0.01 vs GHRP-6 alone) while failed to modify it in young subjects (GH peak: 13.5 +/- 3.4 micrograms/L). The GH response to oral ARG+GHRP-6 in elderly was higher than that to all stimuli in young adults (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the potentiating effect of pyridostigmine, arginine and propranolol on the GHRH-induced GH release in short children

The effect of pyridostigmine (60 mg orally), arginine (0.5 g/kg iv) and propranolol (PROP, 40 mg orally) on GHRH (1 microgram/kg iv)-induced GH release was studied in seven short children. Pyridostigmine and arginine induced a similar potentiating effect on GHRH-induced GH rise (Peak, mean +/- SEM: 56.9 +/- 12.8 and 48.6 +/- 8.5 micrograms/L, respectively vs 12.3 +/- 1.6 micrograms/L; p < 0.05). Combination of GHRH with propranolol induced an increase of GH that was significant only with regard to peak (28.9 +/- 8.4 micrograms/L) but not to AUC. However, GH rises observed after GHRH combined with PD or ARG did not significantly differ from that recorded after coadministration of GHRH and PROP both for peak and AUC. Our results confirm that pyridostigmine and arginine have a striking potentiating effect on the GHRH-induced GH rise in children and show that the tests with GHRH + PD and GH + H + ARG are ore reliable than that with GHRH + PROP to explore the secretory capacity of somatotroph cells.

A neuroendocrinological approach to evidence an impairment of central cholinergic function in aging

A hypothalamic pathogenesis for the reduced GH secretion in aging has been reported for both animal and man. To further address this issue we studied in 31 elderly normal subjects (6 males and 25 females, aged 66-90 yr) and in 22 young healthy controls (13 males and 9 females, aged 20-35 yr) the GH responses to GHRH test (GHRH29, 1 microgram/kg i.v. as a bolus at 0 min) alone and combined with pyridostigmine, a cholinesterase inhibitor (PD, 120 mg po 60 min before GHRH), or with arginine (ARG, 30 g in 100 ml infused from 0 to 30 min). Serum IGF-I levels were lower in elderly than in young subjects (mean +/- SE: 86.9 +/- 7.2 vs 288.7 +/- 22.1 micrograms/L, p < 0.01). The GHRH-induced GH increase was lower in elderly than in young subjects (p < 0.01). PD increased the GH response to GHRH in both groups (p < 0.001), but in elderly subjects this response persisted lower (p < 0.0001) than that observed in young adults. Also ARG coadministration potentiated the GHRH-induced GH release in both groups (p < 0.0001) but in this case the elderly's responses overlapped with the young's. The GH increase observed after combined administration of ARG and GHRH was higher (p < 0.0001) than that elicited by PD plus GHRH in elderly but not in young subjects. Analyzing individual GH responses, a GH peak below the limit of normality for young adults was observed in 19 (61.3%) elderly subjects after PD plus GHRH administration while ARG plus GHRH test elicited a normal GH peak in all but one.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine potentiates but does not restore the blunted growth hormone response to growth hormone-releasing hormone in obesity

A blunted growth hormone (GH) response to several stimuli, including growth hormone-releasing hormone (GHRH), has been shown in obesity. Arginine (ARG) has been demonstrated to potentiate the GHRH-induced GH increase in normal subjects, likely acting via inhibition of hypothalamic somatostatin release. To shed further light onto the mechanisms underlying the blunted GH secretion in obesity, we studied the effect of ARG (0.5 g/kg infused intravenously [IV] over 30 minutes) on both basal and GHRH (1 micron/kg IV)-stimulated GH secretion. Eight obese subjects (aged 26.4 +/- 3.9 years; body mass index, 39.0 +/- 1.9 kg/m2) and eight normal control volunteers (aged 27.0 +/- 1.7 years; body mass index, 22.3 +/- 0.5 kg/m2) were studied. In obese subjects, the GH response to both GHRH and ARG was lower (P less than .01 and P less than .002, respectively) than in controls. ARG potentiated the GH response to GHRH in obese patients (P less than .0003). However, in these patients, the GH secretion elicited by GHRH, even when coadministered with ARG, persisted at reduced levels (P less than .005) when compared with controls. Basal insulin-like growth factor-1 (IGF-1) levels did not significantly differ in obese subjects and in normal subjects (161.1 +/- 37.0 v 181.0 +/- 12.8 micrograms/L). In conclusion, ARG enhances the blunted GHRH-induced GH increase in obese patients, but the GH responses to ARG alone and to ARG + GHRH persist at lower levels than in normals. Thus, our results suggest the existence of a reduced pituitary GH pool in obesity.

Galanin reinstates the growth hormone response to repeated growth hormone-releasing hormone administration in man

OBJECTIVE

To clarify the mechanism by which galanin, a 29-amino-acid peptide, increases GH secretion in man.

DESIGN

We studied the GH-releasing effect of this neurohormone (galanin, 15 micrograms/kg) infused over 60 minutes after 120 minutes of saline, following a previous GHRH bolus (GHRH 1 microgram/kg i.v. at 0 minutes, galanin infused from 120 to 180 minutes) and coadministered with the second of two consecutive GHRH boluses (GHRH every 120 minutes, galanin infused from 120 to 180 minutes).

PATIENTS

Fourteen healthy male subjects, aged 20-34 years, in two groups (group A, 20-31 years (n = 8); group B, 25-34 years (n = 6)) were studied.

MEASUREMENT

Blood samples were drawn every 15 minutes of 255 minutes. Serum GH was measured in duplicate by IRMA. Statistical analysis of the data was carried out by non-parametric ANOVA test.

RESULTS

The GH response to galanin infused 120 minutes after saline overlapped with that induced by the neuropeptide infused following previous GHRH bolus (AUC, mean +/- SEM: 317.3 +/- 73.2 vs 326.8 +/- 54.2 micrograms/l/h). The GH-releasing effect of the second GHRH bolus (126.9 +/- 32.3 micrograms/l/h) was lower than that of the first one (503.4 +/- 41.3 micrograms/l/h; P = 0.0002). Galanin markedly enhanced the GH responses to the second GHRH bolus (1118.0 +/- 212.7 micrograms/l/h; P = 0.0002 vs second GHRH bolus alone) so that it did not significantly differ from the first one (710.9 +/- 107.8 micrograms/l/h).

CONCLUSIONS

Our results show that the GH-releasing effect of galanin is not modified by GHRH pretreatment and that the neuropeptide reinstates the GH response to the repeated GHRH stimulation in man. They suggest that these effects are due to the inhibition of hypothalamic somatostatin release.

Arginine reinstates the somatotrope responsiveness to intermittent growth hormone-releasing hormone administration in normal adults

It is well known that in normal adults the growth hormone (GH) response to GH-releasing hormone (GHRH) is inhibited by previous administration of the neurohormone. In 7 healthy volunteers (age 20-34 years) we studied the GH responses to two consecutive GHRH boluses (1 microgram/kg i.v. every 120 min) alone or coadministered with arginine (30 g i.v. over 30 min). The GH response to the first GHRH bolus (area under the curve, mean +/- SEM: 506.3 +/- 35.1 micrograms/l/h) was higher (p = 0.0001) than that to the second one (87.1 +/- 14.6 micrograms/l/h). The latter response was clearly increased (p = 0.0001) by coadministering arginine (980.5 +/- 257.5 micrograms/l/h). When every GHRH bolus was combined with arginine a marked potentiation of GH response to both boluses was found. However, the second combined administration of arginine and GHRH induced a GH increase which was lower compared to the first one (p = 0.016). In conclusion, our results show that arginine potentiates the GHRH-induced GH secretion preventing the lessening of somatotrope responsiveness to the neurohormone alone. As there is evidence that this phenomenon is due to an enhanced somatostatin release, these findings give further evidence of a somatostatin-suppressing effect of arginine.

Pyridostigmine potentiates L-dopa- but not arginine- and galanin-induced growth hormone secretion in children

The coadministration of growth hormone (GH) secretagogues can provide insight into the neuroregulation of GH secretion. The GH response to L-dopa (125, 250 and 500 mg orally for body weights less than 15 kg, between 15 and 30 kg and greater than 30 kg, respectively), arginine (Arg; 0.5 g/kg infused intravenously over 30 min) and galanin (GAL; 15 micrograms/kg infused intravenously over 60 min) when administered alone or combined with pyridostigmine (PD; 60 mg orally), a cholinergic agonist that likely acts via inhibition of endogenous somatostatin secretion, was studied in children with familial short stature. The GH-releasing effect of PD was also evaluated. In 8 children, PD and L-dopa when administered alone induced an equivalent GH rise (area under the response curve, mean +/- SEM: 241.4 +/- 31.1 vs. 202.9 +/- 38.6 micrograms/l/h) while their coadministration had an additive effect (435.4 +/- 41.4 micrograms/l/h; p less than 0.02 vs. PD and L-dopa alone). On the contrary, in other 8 children, PD and Arg induced similar GH increases either when administered alone (394.2 +/- 68.5 vs. 405.8 +/- 103.9 micrograms/l/h) or in combination (535.8 +/- 97.3 micrograms/l/h). GH increases almost superimposable were also observed when PD and GAL were administered alone (405.2 +/- 72.3 vs. 412.6 +/- 94.1 micrograms/l/h) or in combination (537.9 +/- 139.0 micrograms/l/h) in other 7 children. These data show that the enhancement of the cholinergic activity by PD increases the L-dopa-induced GH release but fails to modify both Arg- and GAL-induced GH release in short children.(ABSTRACT TRUNCATED AT 250 WORDS)

A new test for the diagnosis of growth hormone deficiency due to primary pituitary impairment: combined administration of pyridostigmine and growth hormone-releasing hormone

The diagnosis of growth hormone (GH) deficiency (GHD) is currently based on failure to increase plasma GH levels to an arbitrary cutoff point of 7 or 10 micrograms/l in response to two provocative stimuli. False negative responses to these tests, however, frequently occur thus reducing their diagnostic reliability. The aim of this study was to assess a combination of pyridostigmine (PD) and GH-releasing hormone (GHRH) (60 mg oral PD 60 min before 1 microgram/Kg GHRH iv) as a reliable test probing pituitary somatotropic function. In fact PD, an acetylcholinesterase inhibitor, strikingly potentiates GH response to GHRH likely by inhibiting somatostatin release. The combination PD + GHRH was tested in normal children and adolescents (NS, n = 27) and in a large group of short children classified as having familial short stature (FSS, n = 24), constitutional growth delay (CGD, n = 34) and GH deficiency (organic, oGHD, n = 6; idiopathic, iGHD, n = 10). In all groups results obtained by PD + GHRH were compared with those obtained by testing with GHRH, clonidine (CLON) and PD alone and by studying spontaneous nocturnal GH secretion over 8 hours. Assuming 7 micrograms/l as minimum normal GH peak, a positive response occurred in only 18/24, 11/12 and 12/13 NS for GHRH, CLON, and PD, respectively. In contrast even assuming a minimum normal GH peak as high as 20 micrograms/l, PD + GHRH induced a positive response in 27/27 NS all having a nocturnal GH mean concentration (MC) greater than or equal to 3 micrograms/l. Therefore PD + GHRH test gave no false negative responses and this was true not only in NS but even in all FSS and CGD having a GH MC greater than or equal to 3 micrograms/l. On the other hand, PD + GHRH induced a negative GH response in all oGHD and in 8/10 iGHD patients. In the remaining two iGHD patients, PD + GHRH demonstrated a normal pituitary GH reserve in spite of a GH MC less than 3 micrograms/l and low IGF-I level, thus pointing to a hypothalamic pathogenesis for the GHD. Considering FSS and CGD children having a GH MC less than 3 micrograms/l, PD + GHRH showed a primary pituitary GH deficiency in 3/12 CGD with low plasma IGF-I levels. In conclusion, in slowly growing children PD + GHRH test is the most reliable provocative test for the diagnosis of primary pituitary GH deficiency being capable to discriminate between an unequivocally normal and impaired somatotropic function.(ABSTRACT TRUNCATED AT 400 WORDS)