Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. The particular effect of mediator depends on many circumstances i. It may also undergo contraregulation.
The majority of those hormones play an important role in the pathogenesis of CVS diseases', which can result in the development of new medicines. Abstract Hormones have an influence on many tissues and organs, including the cardio-vascular system CVS. Publication types English Abstract Review. Abnormalities of cardiac structure and function have also been demonstrated in GH-deficient GHD patients 9 — 11 , which may also predispose to their increased cardiac mortality.
Cardiac autonomic tone can be assessed from heart rate variability HRV , i. Patients with known abnormalities in cardiac structure, such as after myocardial infarction 15 , 16 and congestive cardiac failure 17 , have changes in cardiac autonomic tone that can be measured using power spectral analysis PSA of HRV. Using this technique, a spectral graph is obtained, and the area under the curve for each frequency band is defined as the power for that frequency range.
HF power is generally considered a marker of vagal activity, and LF power is considered to be due to sympathetic activity 12 , 13 , The origin of VLF remains controversial and may be related to thermogenesis 18 , the renin-angiotensin system 12 , 19 , or peripheral chemoreceptors As cardiac abnormalities have been shown to be present in GHD patients, it is possible that cardiac autonomic dysfunction may coexist in these patients, and we, therefore, compared HRV measurements between GHD patients and a matched group of healthy controls.
Fourteen GHD patients nine women and five men; aged 19—56 yr; average, Five patients four women and one man had developed GHD in childhood, and nine five women and four men had adult-onset GHD. The diagnoses and treatments for these patients are listed in Table 1. The estimated duration of GHD was 6. Symptoms such as tiredness, fatigue, and lack of concentration were present in these GHD patients, all of whom were being considered for GH treatment.
In fact, the GH response in all patients was less than 2. These GHD patients had no significant medical illness and, apart from pituitary hormone replacement, were not taking any other medication.
The GHD patients were compared with a group of normal healthy volunteers, who were matched for age, sex, and body mass index Table 2. The healthy controls did not have any significant medical problems and were not taking any medication. All patients and controls had normal renal function and fasting blood glucose. The GHD patients all had free T 4 levels within the normal range mean, For the control population, normal thyroid function tests were defined as a normal TSH level mean, 2.
This study had the approval of the local ethics committee, and all subjects gave their informed consent. All tests were performed in the morning between — h with the subjects fasted overnight. No cigarettes, alcohol, or caffeine-containing drinks were taken for 24 h before the tests. All subjects were tested for cardiac autonomic dysfunction with an automated device This measures R-R interval data during a standard set of heart rate variability tests as described by Ewing and Clarke In addition, the blood pressure response to standing from a supine position was measured.
Normal results with the four tests were as defined by Ewing and Clarke 25 and Sundkvist The tests were performed in a quiet temperature-controlled 18—22 C room.
At the end of 15 min, three blood pressure readings were obtained using the Omron Corp. The average heart rate over the duration of ECG recordings 15 min was also calculated in all subjects. The ECG signals were analyzed off-line. After manually excluding all ectopic beats, the data were resampled at 2 Hz, and the Hamming spectral window was employed to reduce spectral leakage The FFT method was used for the calculation of the power spectral density. The advantages of this method are the simplicity of the algorithm used FFT and the high processing speed Three different frequency bands VLF, 0—0.
The area under the power spectral density curve is the power of each frequency band. The total spectral power 0—0. For nLF and nHF, the total power is defined as the power between 0. The normalization process was used because it provides a reliable quantitative estimate of autonomic balance The heart rate variability data between groups were analyzed using the Mann-Whitney U test, and the rest of the data were analyzed using unpaired t tests.
This study had the approval of the local ethics committee, and all subjects and patients gave their informed consent. The demographic details of GHD patients and controls are shown in Table 2. There was no difference in diastolic pressures or resting heart rate between the two groups. No abnormalities in cardiac autonomic function were detected in either group of subjects using standard autonomic tests 25 Table 3. Typical power spectral graphs obtained from a GHD patient and a healthy control are shown in Fig.
Typical spectral graphs obtained from a GHD patient and a control subject. The area under the curve is the power of that particular frequency band. Results of the autonomic function tests performed on GHD patients and the control group.
Normal values are shown in parentheses. The results were analyzed by Mann-Whitney U tests. No significant difference was detected between the two groups. Absolute total power 0—0. However, when the power within each frequency band was normalized, significant differences in all three main frequency bands VLF, LF, and HF were demonstrated between the two groups Table 4 and Fig. All data were analyzed using Mann-Whitney U test.
NU, Normalized units. Interestingly, the standard autonomic function tests 25 detected no evidence of cardiac autonomic neuropathy in the GHD patients. A potential variable accounting for the differences we observed is the effect of other hormonal replacement therapy, such as T 4 and corticosteroid. However, subgroup analysis of the GHD patients showed that the differences in HRV compared to controls still existed regardless of whether the GHD patients were taking T 4 or corticosteroid.
A previous study examining the peripheral sympathetic nervous system in GHD patients reported increased muscle sympathetic nerve activity MSNA in GHD patients compared with controls, as measured by microneurography However, we have shown that cardiac sympathetic activity is low in this group of patients.
Two different components of the sympathetic nervous system are being assessed by the two techniques; MSNA is a measure of peripheral sympathetic activity, and HRV is a measure of cardiac autonomic tone. In healthy volunteers, there is good concordance between MSNA and HRV 30 , but in subjects with structural cardiac damage, such as those with heart failure 31 , 32 , there is high peripheral sympathetic activity raised MSNA but low cardiac sympathetic tone low LF.
It is possible that activation of the sympathetic nervous system is nonuniform and may be reduced in certain regions in GHD patients. The hypothalamus is part of the central autonomic network 34 , and animal studies have demonstrated that sympathetic activity can be increased by insulin 35 , but this is regional 35 , Similarly, GH may also increase sympathetic nervous activity via the hypothalamus in a regional distribution.
Secondly, the GHD patients in the two studies differed in several respects. In addition, there was no difference in the blood pressure of the GHD patients in that study and that of the controls; in the present study the GHD patients had significantly lower systolic blood pressure compared to controls. It is also possible that the abnormalities in HRV detected in our subjects are a consequence of abnormal cardiac structure due to GH deficiency.
Previous studies have shown that cardiac structural abnormalities, such as decreased left ventricular mass and reduced left ventricular ejection fraction, can be present in GHD patients 9 — 11 , 37 — These cardiac abnormalities may reduce the ability of the heart to respond to the sympathetic nervous system.
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