Growth hormone is a polypeptide hormone synthesised and secreted by the anterior pituitary gland which stimulates growth and cell reproduction in humans and other vertebrate animals.

GH is released from the pituitary into the bloodstream in a pulsatile manner under the regulatory control of hypothalamic somatostatin (SS) and GH-releasing factor (GHRF).

Stimulators of GH secretion include, exercise, hypoglycemia, dietary protein, and estradiol. Inhibitors of GH secretion include dietary carbohydrate and glucocorticoids. 

Almost 50% of GH in circulation is bound to a high affinity GH binding protein (GHBP), which represents the extracellular domain of the GH receptor. 

The plasma concentration of GH during these peaks may range from 5 to 30 ng/ml or more. Peaks typically last from 10 to 30 minutes before returning to basal levels. The largest and most predictable of these GH peaks occurs about an hour after onset of sleep. Otherwise there is wide variation between days and individuals. Between the peaks, basal GH levels are low, usually less than 3 ng/ml for most of the day and night.

The amount and pattern of GH secretion change throughout life. Basal levels are highest in early childhood. The amplitude and frequency of peaks is greatest during the pubertal growth. Healthy children and adolescents average about 8 peaks per 24 hours. Adults average about 5 peaks. Basal levels and the frequency and amplitude of peaks decline throughout adult life.

The primary biological actions of the hormone are in direct growth promoting. HGH exerts its effect directly on target organs such as cartilage, bones and muscles and indirectly through the release of insulin-like growth factor (IGF), produced in the liver (2). In particular, somatotropin C (IGF-1) is essential for bone growth during childhood.

Generally GH increases protein synthesis and stimulates the growth of all internal organs excluding the brain. GH reduces liver uptake of glucose, an effect that opposes that of insulin. GH also contributes to the maintenance and function of pancreatic islets. GH stimulates the immune system. GH can cause excessive growth, traditionally referred to as pituitary gigantism.

Deficiency of GH produces significantly different problems at various ages. In children, growth failure and short stature are the major manifestations of GH deficiency. In adults the effects of deficiency are more subtle, and may include deficiencies of strength, energy, and bone mass, as well as increased cardiovascular risk.

Diagnosis of GH deficiency involves a multiple step diagnostic process, usually culminating in GH stimulation test(s) to see if the patient's pituitary gland will release a pulse of GH when provoked by various stimuli.

May be diagnosed by:

• Determination of specific antibodies based on the ELISA technique
• Determination of specific antibodies based on the RIA-technique

HGH ELISA:

Immunoenzymatic colorimetric method for quantitative determination of HGH in human serum.

Principle of the Assay:

In this method, calibrators, patient specimens and/or controls containing the native hGH antigen are first added to streptavidin coated wells. Biotinylated monoclonal and horseradish peroxidase (HRP) labelled antibodies are added and the reactants are mixed. The different types of antibodies used have high affinity and specificity and are directed against distinct and different epitopes of hGH. Reaction between the various hGH antibodies and native hGH occurs in the microwells without competition or steric hindrance forming a soluble sandwich complex.

The interaction is illustrated by the following equation:

 
BtnAb(m)   Byotinilated Monoclonal Antibody (Excess Quantity)
AgGH   Native Antigen (Variable Quantity)
HRP-Ab(p)  HRP labeled Antibody (Excess Quantity)
HRP-Ab(p)-AgGH-BtnAb(m) Antigen-Antibodies Sandwich Complex
Ka   Rate Constant of Association
K-a   Rate Constant of Dissociation

Simultaneously, the complex is fixed to the well through the high affinity reaction of streptavidin and biotinylated antibody. This interaction is illustrated below: 

Streptavidin CW = Streptavidin immobolized on well.
Immobilized Complex = Antibodies-Antigen sandwich bound.

After equilibrium is attained, the antibody-bound fraction is separated from unbound antigen by aspiration. The native antigen concentration is directly proportional to the HRP activity in the antibody-bound fraction. The activity of the conjugated HRP is quantitated by reaction with TMB substrate to produce blue colour. The reaction is terminated by adding stop solution which turns the blue colour into yellow. The absorbance is measured on a plate reader.

Specific performance characteristics: 

Correlation with RIA performed on 54 samples is r = 0.99

Order information: