THE NATURE OF hGH SECRETAGOGUES
"Attention to health is life's greatest hindrance."
"Plato was a bore."
Secretagogue: that which stimulates secreting organs. Many substances
stimulate the release of growth hormone from the pituitary gland. Amino
acids, drugs, and exercise are among the provocateurs. Despite the
phenomenal success of synthetic GH, scientists are in hot pursuit of
factors that can be taken orally to stimulate the pituitary to release GH.
Recombinant GH is problematic: it has to be injected-in most cases several
times a day. It is expensive-way outside the budget of many people who
would otherwise benefit. It has side effects and probably down regulates
receptors, which means that its effects diminish over time. Researchers
realize that what is needed is something that can be taken orally to
stimulate the natural secretion of GH. This must be accomplished in a way
that will prevent over stimulation to the point of down-regulation, but at
the same time increase the hormone to a level that will elicit a response.
Some of the important advantages to GH secretagogues include preservation
of feedback mechanisms that modulate GH response and generation of
pulsatile patterns of GH release, which more closely mimic natural
Congestive Heart Disease
Carpal Tunnel Syndrome
Reduced Insulin Sensitivity
Leukemia in Children
Possible Side Effects Associated with GH Injections
The Evolution of Secretagogue Research
Synthesis of GH in the '80s. led to an explosion of GH research. The
list of potential beneficiaries grew to include AIDS patients, burn
victims, patients with Turner's syndrome, those receiving glucocorticoids
and chemotherapy, and of course the elderly.
While some researchers pursued the effects of injected synthetic GH,
others focused on finding GH secretagogues.
In 1977, Dr. Roger Guillemin was awarded the Nobel Prize for his work on
GH. Guillernin discovered the two hormones that are known to control GH.
Both originate in the hypothalamus. One is called growth hormone releasing
hormone (GHRH) and the other is somatostatin. GHRH stimulates growth
hormone release, while somatostatin inhibits it.
The discovery of these hormones marked the recognition of auxiliary
substances that would affect GH status,
and initiated a search for the perfect secretagogue.
The Morphine Connection
Frank Momany, Cyril Bowers and their group discovered the first
synthetic secretagogue. It was called growth hormone releasing peptide 6
(GHRP-6) in reference to its six constituent amino acids. Strangely
enough, the discovery of GHRP-6 came from research on morphine addiction.
In the 1920s, it was noted that female morphine addicts were often
sterile. A few curious scientists tried to study the phenomenon by
recreating the situation in rats. But no matter how much morphine they
injected, sterility could not be induced. In 1934, a researcher named Ko
tried it in mice and it worked. Three years later another researcher, Dun,
did the same in rabbits with the same result. But because the model
couldn't be recreated in rats, researchers shied away from studying it
In 1949, Dr. Charles Barraclough and his colleague Everett discovered
that the hormone that induces the reproductive cycle is released only at a
certain time of the day. Previous researchers had been injecting rats at
the wrong time! Barraclough and another colleague, Sawyer, quickly
demonstrated that if given at the right time of the day, morphine blocked
the reproductive cycle in rats. At that time, they theorized that the
signal that caused the pituitary to release the reproductive hormone
originated in the hypothalamus. While it didn't seem very significant at the
time, the knowledge that morphine affected pituitary hormone eventually
became very important.
In 1972, Dr. Paul Cushman was looking to define more specifically the
effect that morphine has on the pituitary.
At that time, GH was considered the "most sensitive index of pituitary
function". So Cushman set up studies to measure GH in morphine addicts.
Unfortunately, because of problems in methodology and the small number of
he could draw no sound conclusions about the effects of morphine on the
pituitary or GH. But the first inkling that GH is under control of an
opioid was had. The following year, researchers at the University
California, Irvine demonstrated conclusively that morphine increases GH.
Three years later, it was shown that morphine initially increases GH
levels, then causes them to decline.
That same year, researchers found "natural" morphine in the body, and the
pieces of the puzzle started coming together. Did natural morphine, like
synthetic morphine, increase GH? Later that year, Dr. John Hughes and his
group synthesized natural morphine. It turned out to be two pentapeptides
(5 amino acids). They called the substance "enkephalin". Enkephalin caused
the release of GH. It was a natural secretagogue. For the next 5 years,
dozens of researchers shuffled the amino acid sequence of enkephalin,
hoping to find a GH secretagogue they could patent. Many analogues of
enkephalin were reported to increase GH, but nothing was pursued for
commercial use. Gradually, most researchers abandoned the hunt for the
Momany and Bowers of Tulane University continued refining their
sequences until finally, in 1979, they came up with a peptide that was
active orally. The hexapeptide (6 amino acids) was known as "growth
hormone releasing peptide-6" (GHRP-6). The peptide is:
His-DTrp-Ala-Trp-DPhe-LysNH2. Although GHRP-6 was active when taken
orally, it didn't cause enough GH enhancement to be patented and sold as a
drug. Momany, Bowers and others have used GHRP-6 as a launching pad to
create other, more potent secretagogues. One of them, Hexarelin, is
currently undergoing trials. Momany continues to study potential
secretagogues for GH and other hormones, using sophisticated computer
modeling to combine and recombine the amino acids.
You may note the "D" prefix to some of the amino acids in the GHRP-6
sequence. This is common to all major secretagogue peptides that have been
studied. The natural form of these constituent amino acids is the "L"
but for proprietary and stability reasons-they have been replaced with the
synthetic "D" form. This is not the case
with the naturally derived peptide secretagogues that we will describe
GHRP-6 and its derivatives are peptide secretagogues, but non-peptide
secretagogues have been created.
Using molecular modeling, researchers at Merck have designed a drug
(presently known as MK677) that mimics
the effect of GHRP-6. It works by artificially inducing similar kinds of
changes in' cell membranes caused by GHRP-6.
Its chemical structure is similar to benzodiazepine drugs.
It is interesting to note that, like growth hormone injections, none of
the synthesized secretagogues address the systemic influences of GH such
as IGF-1 1 formation and receptor sites. This probably explains the mixed
results that they have produced in terms of consistent IGF- 1 stimulation
and the lack of symptomatic improvement, which have impeded their success.
In this assessment, we cannot ignore the natural GH secretagogues that
originate within the body (endogenous) and outside the body (exogenous).
Estrogen and testosterone enhance GH, as do the amino acids arginine and
The vitamin niacin (B3, niacinamide) enhances GH by reducing free fatty
acids. Fasting enhances GH, and so does intense, sustained exercise.
However, none of these by themselves increase GH enough, or in the proper
way, to be considered a true GH enhancement therapy. But, as you are about
to discover, the proper combination of peptides, pharmaceutical sugars,
amino acids, diet, and exercise can produce significant and measurable age
reversing effects. And it's a lot simpler than it sounds.
Intrinsic Factors that Affect GH Release
There are several factors that control GH release in a manner that may
limit response to secretagogue therapies.
We have reviewed the hypothalamic hormones, GHRH and somatostatin, and
their direct role in regulating GH secretion, but GH regulation is far
more complex. In addition to pituitary receptors for which corresponding
hormones have not yet been identified, there are direct influences that
come from each of the minerals potassium, magnesium, calcium, and zinc.
The dominant memory neurotransmitter, acetyl-choline, regulates GH
secretion, while blood pH and feedback mechanism from IGF-1 and IGF-2 play
important roles. Other factors, such as hGH binding proteins and metabolic
clearance rate directly limit symptomatic response to growth hormone.
These are only some of the intrinsic factors that have been identified,
and upon examining them, we begin to gain an appreciation for the years of
research that have been performed on hGH secretagogues and the complexity
a substance that works not only to elicit GH release, but consistent
Model depicting the pathways responsible for the GHRH - induced
increase in [Ca+ +], and GH release in somatotrophs.
This graphic representation illustrates some of the known mechanisms by
which calcium (Ca++) elicits the release of GH from pituitary
somatotrophs. Ca++ increase is associated with an increase in GHRH.
Interestingly, any rise in Ca++, independent of GHRH, will cause the
release of GH, and any fall in Ca++ will cause a diminished release of GH.
The pulsatile secretion pattern of growth hormone has been directly
associated with rhythmic rises in Ca++. One of the mechanisms by which
somatostatin works to block GH secretion is through inhibition of Ca++ and
potentiation of potassium (K+).
Zinc deficiency is known to profoundly affect the GH/IGF-I axis. Many
of the signs of zinc deficiency are directly associated with the action of
growth hormone, including poor wound healing, reduced protein synthesis,
immuno-suppression, and reduced hormone concentrations. Zinc, magnesium,
and potassium deficiencies can all negatively affect circulating IGF-1.
In addition to the intricacies involved in its release, there is a
great degree of complexity associated with the growth hormone molecule
itself. Although most attention in focused on 22-kd hGH, "free GH", which
accounts for only 20% of the over 100 naturally occurring forms of hGH
that have been identified, the role of the other 80% of various forms of
hGH is not yet fully understood. Research shows that GH bound to growth
hormone with GH binding protein (hGH(hGHbP)2 plays an important role in
maintaining and enhancing the activity of growth molecule hormone.
Interestingly, the hGH(hGHbp)2 is structurally identical to the free form
of porcine growth hormone -the form that is predominant in the porcine
pituitary, a primary ingredient in Symbiotropin.
Some of the details, which we have merely brushed the surface of here,
begin to give us a flavor for the complexity of an effective GH
secretagogue. Individual amino acids, vitamins, peptides and prescription
drugs may bring about some type of GH release, but without creating the
proper environment, results are limited.
I do not have to get up to urinate at night
- O.B. (Male, Age 76)
I had severe emphysema, and it has improved
- F.B. (Male, Age 67)